Sam Taylor Wood and 20-year-old fiancé Aaron Johnson welcome baby girl Wylda

Artist-turned-film director Sam Taylor Wood and her actor fiancé Aaron Johnson are celebrating after welcoming a baby girl, whom they've named Wylda Rae.

The happy news was confirmed by Aaron's Kick Ass co-star Christopher Mintz-Plasse, who wrote on his Twitter account: "Crazier news. Aaron Johnson's baby was born!! So exciting!"

Forty-three-year-old Sam and Aaron have been engaged since October after they met on the set of Nowhere Boy, in which Aaron plays a young John Lennon.

Much has been made of the age gap between them, but Sam – who has twice beaten cancer - has dismissed it, saying: "This whole age thing is abstract to us anyway. We don’t ever think about it. He’s more mature now than are a lot of men my age."

For his part, Aaron says: "She's a young soul and I'm an old soul"

The new arrival is the third child for Sam, who already has two girls, 13-year-old Angelica and Jessie, five, from her 11-year marriage to art dealer Jay Jopling. That relationship came to an end in September 2008.

Aaron lives with his fiancée and her daughters in an £11 million townhouse in north London. It's thought Sam bought the property using part of her divorce settlement.