London, Apr 25 : Mel Gibson's wife filed for divorce after hearing his Russian lover say she is pregnant, it has been revealed.

It is said that Robyn, 53, decided to end their 28-year marriage after Oksana Grigorieva told pals she was expecting.

She was also stunned to find the Braveheart star had moved Grigorieva and her son, 11, into one of his mansions in California.

"Robyn put up with Mel for years but when she found out Oksana was telling friends she was expecting it was the last straw," the Sun quoted a source as saying.

"Robyn wants a `quickie' divorce, one that isn't contested, with their assets divided later," the source added.

Oksana was yesterday spotted outside Gibson''s mansion chatting on her mobile with what appeared to be a baby bump under her pink shirt. (ANI)