The centenary of Walt Disney's birth, due to be celebrated next week, has been overshadowed by a controversy over his real birth date and the theory that he may have been the illegitimate child of a Spanish washerwoman.

The Disney family has consistently rejected claims that the genius of cartoon moving pictures was anything other than the legitimate child of Elias and Flora Disney, born in their home in Chicago on December 5 1901.

But the lack of a birth certificate for Walt and a 60-year-old legend in the southern Spanish town of Mojacar have led to renewed speculation that he may have been the love-child of washerwoman Isabel Zamora. She allegedly went to live with her brother in Chicago and allowed the boy to be secretly adopted by the Disney family.

The first record of Walt Disney's existence is found on a baptism ledger at St Paul's Church, Chicago, in June 1902, which puts the birth date as December 5, 1901. Flora Disney signed sworn affidavits in 1918 and 1934 saying Walt had been born at their home.

That version of events was first challenged in 1993 by Marc Eliot, author of an unauthorised biography, Walt Disney: Hollywood's Dark Prince.

He unearthed documents signed by FBI chief Edgar Hoover which, he claimed, showed that the creator of Mickey Mouse, Donald Duck, Dumbo and Bambi had doubts about his own origins.

Now another unauthorised biographer, Christopher Jones, is working on the theory that Walt Disney was actually the illegitimate son of Mojacar's eccentric doctor, Gines Carrillo, and Isabel Zamora.

"The fact is that Walt Disney is probably the washerwoman's illegitimate son," says Jones, son of former Disney press agent Tom Jones.