A biographer who made a bombshell revelation of Freddie Mercury's secret daughter has reassured fans she is telling the truth.

Bestselling author Lesley-Ann Jones has faced questions from some aficionados of the late singer and his band Queen after revealing the child's existence in a new book.

The Mail told on Saturday how her new book called Love, Freddie, reveals the daughter was conceived accidentally during a fling with the wife of a close friend in 1976, a year after the group's most famous song Bohemian Rhapsody was first a hit.

Her existence was known only to Mercury's closest circle, including his parents and sister, the rest of the band members and the love of his life Mary Austin.

The girl, who is now 48 and lives in Europe, where she is a medical professional and also a mother – making Freddie a posthumous grandfather, according to the book.