Movie mogul Steven Spielberg's actress stepdaughter Jessica Capshaw has given birth to her third child.

Capshaw and her husband Christopher Gavigan became parents to a baby girl on Wednesday.

The Grey's Anatomy star's half sister Sasha - Spielberg's daughter by Capshaw's mother Kate - revealed the news by sharing online a picture of herself holding the new addition, writing, "Welcome niece".

The couple wed in 2004 and is already parents to Eva Augusta, 20 months, and Luke Hudson, four.