Acclaimed filmmaker and actress Sarah Polley says a painful family secret inspired her new documentary, “Stories We Tell.”

The Toronto-based star says she had long suspected her late mother, who died when Polley was 11,  may have had an   affair that led to her conception.

A  DNA test in 2006  confirmed that a man she had met almost by accident was her biological father.

Polley  hid the information for a year and revealed it to  the father she grew up with  after learning that  a journalist  had discovered her  secret.

Blogging on the National Film Board of Canada website, the Oscar-nominated writer-director reveals that  she made the film   after learning the identity of her biological father.

“Stories We Tell”  premiered today  at the Venice Film Festival.