I think it must be an Urban Myth(sorry)
Stewart Granger only had 3 children.
Tracy Granger,Mother was Jean Simmons.
Jamie and Lindsey,Mother was Elspeth March.
Of course if she washis illigitimate child we probably wouldn't wouldn't know.
Bunny has it seems an "awful" first name (she hates it so) she has offered a prize to anyone on the Antiques Roadshow team who can find out what it is.
A small piece of trivia about Bunny.
She is the Great Grand Daughter of Luigi Lablache,one of the greatest of 19th Century Operatic Basses.
He even gave singing lessons to Queen Victoria.
See here:~
http://en.wikipedia.org/wiki/Luigi_Lablache
Going by her exotic ancestry I would imagine she has an equallexotic first name?