“If I close my eyes,” Jennifer Hudson says, closing her eyes, “I can almost remember what it was like, what I was like, 15 years ago. I was at home in Chicago, still in high school, singing in church, living with my family.” She opens her bright brown eyes again, stares straight at me to answer my question. “But generally, no, it feels like another Jennifer life. I don’t look the same. I’m a mother now. So many things have changed. I sometimes think the only constant is my voice. That hasn’t gone away.”

In those 15 years, Hudson has lived more than a few American dreams and nightmares. Having taken her chances at manufactured fame on Simon Cowell’s American Idol (she was a losing finalist in series 3) she discovered it for real with her unforgettable debut acting performance in Dreamgirls, in which she played spurned Motown diva Effie White, stealing the show from Beyoncé Knowles, Eddie Murphy and Jamie Foxx and winning a best supporting actress Oscar. She followed that with a Grammy award-winning album that saw her bracketed, naturally, with Aretha and Whitney. The talk then was that she had an old soul voice, a seen-it-all voice (the authentic sound of a “religious, transcendent experience” Oprah Winfrey said). As it turned out, she hadn’t seen anything yet.

In October 2008, while on tour, Hudson received a call from her sister Julia that changed the narrative of her life forever. Hudson had been trying to reach her mother by text that morning and was worried that she did not get a reply (they contacted each other first thing every morning when she was on the road, so the silence was odd). The silence was explained by Julia’s hysterical call that told her their mother, Darnell, and brother, Jason, had been shot and murdered at home, and that Julia’s seven-year-old son, Julian, was missing.

Hudson later recalled in the trial of her former brother-in-law, William Balfour, that she had gone straight back to Chicago and holed up with her sister in a hotel room, holding each other and waiting for news. After three days, Julian’s body was discovered in the back of a stolen pick-up truck. Balfour was eventually convicted of the three murders in 2012 and received three life sentences.

Hudson is still finding ways to talk about those years. “I have definitely seen the highest of the highs and the lowest of the lows,” she says. “You don’t know how strong you are until you are placed in that kind of moment.” She pauses. “I don’t really know what else to say.”

Her mother had been the secretary of the local church, where Hudson had led the gospel solos in the choir. Was her religious faith a help to her? “It was the ultimate help to me,” she says. “We always said: ‘If He brings you to it, He will bring you through it.’ There would be no point in faith if it wasn’t tested. My mother always told me no matter how negative your life seems to be, you must always look for a positive. That is what I believe a woman of faith should do.”

In hudson’s early years her father was mostly absent from the family and she shared a bed with her mother until she was 16. There is a kind of primal scream of human separation that her voice seems created for. It was there already in her extraordinary performance of Dreamgirls’s signature lament – “And I am telling you I’m not going” – and it is there throughout her second album, on tracks like “I Remember Me”. Her third album, JHUD, which is released in September, includes a song that she has written in her mother’s memory called “Moan”. The lyric runs: “My momma taught me everything I know, and I will take it everywhere I go, if you think you’ve seen it all, just keep on living, live long”.

I imagine the act of singing that song has been very tough. “Yes,” she says, “but Mom would always tell us if you are hurting, moan and you will feel better. That’s the title of the song. There is not a day that goes by when I don’t repeat the things she said. She was very quiet. The complete opposite of us kids. Now she has gone, I realise she had a lot to say. My brother, too, I hear him, too. When we were kids any time my brother saw me crying he would be like, ‘Jenny, knock it off.’ And that’s what I hear him say when I cry now.”

In the immediate aftermath of the tragedy, Hudson was in something of a daze. She was in something like that state, too, she recalls, when she walked out at the Super Bowl in 2012 to sing “Star-Spangled Banner” beside the children of Sandy Hook High School who had lately suffered their own immeasurable loss. The performance came a few weeks after the long process of justice that culminated in the conviction of Balfour.

“In many ways the trial was the most dreadful part of it all,” Hudson says. “But again I know my mother would not have wanted us to miss a beat, so we were there every day. I wouldn’t wish it on anyone to have to experience anything like that, but that is what you do for your family, so that is what we did…”

What was in her head when she stepped out to sing the national anthem? “I was not very present at all any of that time,” she says. “It felt like a dream. I haven’t watched it back, because those moments send you back to a certain place and that’s a place I don’t want to go back to.”

To avoid that constant return to grief, Hudson has worked on ways to live in the present and future. “That is where the Julian D King Foundation came from,” she says, of the charity created in her nephew’s name. “I was thinking how could I find something in all this that would make my mother proud of me. My sister and I lost three family members and we both wanted to find a way that we would not dread every birthday and holiday and family occasion again. I wanted my sister to celebrate Julian’s birthday again, so we created Hatch Day, where we go around together giving local schools supplies that they need. And she looks forward to shopping for that, like she used to look forward to shopping for his birthday presents. My nephew was super into education – he used to call himself Dr King. She can pour his blessings on to these kids and keep his memory alive.”

It is often said of great soul singers that all the grief of the ages is embedded in their voices; have those awful experiences, I ask, changed the way she feels about her own vocal expression? She thinks for a moment. “No,” she says. “Certainly there is a lot of emotion there, but I think I have always been in that kind of space. What do they say in church? Sing from your heart, because you are singing to God. You know, when I used to sing those solos in church I would go through every line and ask the director: ‘What does this mean? What are we trying to convey here?’ If you can’t feel the emotion of a song, how do you expect anyone else to? It’s like a testimony in that way.”

She believes that testimony has become more personal on her new album, which is more upbeat than her previous ballad-led work. “I think this album is more my personality coming through,” she says. She has been writing on some of the tracks and is involved in production, with the help of friends like Timbaland and R Kelly.

“It’s been a completely different experience,” she says. “I’ve never stayed in the studio all night long, but this time I had a three-song set to do with Timbaland and we did all three songs in one night. I was writing, guiding my own vocals, just being creative. I never used to love going into the studio. Now I can’t wait to get there.”

Writing is a new challenge, but the gift of singing has been with her as long as she can remember. When did she first realise she could communicate it?

“When I was 13, 14. It was my other classmates or people in the choir who kind of made me realise,” she says. “They would say the adults listened differently when I sang. And that made me take notice. I started to go and sing at various places and all these people would show up – my teachers, people from church, friends. After that I would be making music videos in the mirror, practising my acceptance speeches. I would sing in the hallway of our home, where the acoustics were good, and neighbours would stop me next morning and say: ‘I heard you singing last night.’ The line was always the same: ‘She’s a little girl but she sounds like a grown woman…’”

There had been a lot of music at home. Her grandmother, who lived with the family, had been a soloist in her time, and taught Jennifer and Julia (“though my sister is not a singer,” Hudson says of her elder sibling, with a rivalrous giggle. “Not at all! She’s hilarious!”)

It was her mother who pointed her in the direction of American Idol. “The first series, I wasn’t so interested. It was summer, I wanted to be outside. But my mother was on at me: ‘You should watch this.’ To start with I was like, ‘Whatever’, but when Kelly Clarkson won the first series I was literally nauseous. I realised it could be for real. I was beating myself up that I didn’t go and audition. When season two came around I had started working for the Disney Cruise Line and that was a given, whereas Idol was a gamble. So I stuck with what I had. I used the ship experience to test myself. When I got off the ship two days later I went to audition for American Idol. That’s when the ball started rolling.”

She must have been surprised not to win.

“It was better to lose, in some ways. When I went to audition for Dreamgirls, I was still in that ‘I am not going to let anything stop me’ kind of mood.”

Was it terrifying to turn up on the first day on set with Foxx and Murphy and Beyoncé, without a day’s acting experience?

“It was like I had blinders on. I had no time to be scared. I didn’t really realise how important my character, Effie, was to the film until it finished, somehow. I just wanted to keep up, make sure I did my best.”

That spirit seems to have been pretty near to the surface throughout Hudson’s life. There is something cheerfully indomitable about her, something you guess will never take no for an answer, and not just because you know what she has come through. When I ask her about her father she says that he wasn’t really present in her childhood, but when she was 14 she thought “enough was enough and went with my siblings to find him. And after that he was around for us until he passed. I was always one for having people get along. So I was a bit like: ‘Let’s go and get Dad and tell him we are all going to live together’ and after that we did. It was kind of weird.”

In 2010 Hudson dramatically changed her appearance, losing 4st and becoming a face of Weight Watchers. I ask if that change in body shape has further changed her sense of self. “I have a lot more fun with clothes and shopping these days,” she says. “But as far as sense of self I have always had a lot of confidence. There were several reasons for it. One was preparing for an acting role. The other was that my fiancé [WWE wrestler-turned-lawyer David Otunga] and I realised that when we were growing up neither one of us had good health examples. We were always told to finish your food, clear your plate. We were never taught the proper way to eat. We grew up around a lot of eating, fish fries on Fridays, all that. When I was ready to have my son we wanted to teach him right. It was not until I went to Hollywood that I realised people might watch what they eat. I was like, ‘Wow!’ And then I thought ‘OK, I can do that.’”

Have people treated her differently?

“Definitely. People I knew 10 years ago, 50lb ago, will be really strange around me. I have to remind them it is me, Jennifer, honestly.”

The birth of Hudson’s son, David Jnr, in 2009, followed quite closely on the tragedy and presented her with a new set of challenges, as well as an ever-present antidote to her grief. She has travelled to London alone when we meet but hates to be away from him.

“He’s nearly five, a big boy now at home with his dad. He will click his fingers when I leave and say, ‘Mum you will be home this quick?’ He’s into superheroes, so I tell him I’m going to fly away like Superman and do my work and fly right back to him. Which works for a while…”

One of the things her experience of being a daughter and mother have taught her is that maybe there are more things to sing about than the songs that tend to come her way. She once expressed her regret, at 30-something, about still being expected to sing exclusively about clubland chemistry. I wonder how strongly she feels that. “Something I said got a bit exaggerated,” she says, “but there are an awful lot of songs about sex, and it’s more like, as I say to my sister Julia sometimes, does everything have to be about that one thing? The world is a broad place. Even on my first album I was like, ‘Isn’t there more to sing about in the world? Or to talk about? There is so much more out there to portray…’”

As she talks, she uses her sister, with whom she has been through so much, as a kind of touchstone, or ever-present confidante. “We have always been very close,” she says. “She works with me now – although she doesn’t do all that much work! She bosses me around, she’s a tough cookie. We don’t live together or anything, she likes being Julia and I like being Jennifer, but she never stops being my big sister. It’s like, ‘Jennifer go get this!’ and I’m like, ‘Hey, I’m the boss!’”

That mixture of tenderness and stubborn will seems ever present in Hudson’s voice. When she was making JHUD her more assertive alter ego was christened with a name – Jones – the part of her that, however broken or vulnerable, is always ready to take on the world. Where, I ask, before our time is up, did that moniker come from?

“It came from doing the shoot for the album,” she says. “The image was coming together photo by photo, but I’d look at it and think: ‘Who is that? It’s not me!’ It took on a whole other persona. It looked more like Grace Jones. Since then I call her Jones, ‘boss lady’, she’s always around.” Hudson laughs. “I don’t think she’s going away any time soon.”

Jennifer Hudson’s latest single, Walk It Out, is out now. The new album is released later this year