According to People, Leigh, 27 and her husband, Nathan West, 30, welcomed a daugter, Anniston Kae a week after shooting wrapped.
The little girl already has two siblings: Noah Wilde, 5, and Taelyn Leigh, 2.
The pregnancy was not written into the “Grey’s Anatomy” storyline.
Leigh plays Lexie, the little sister of Meredith Grey, who’s played by Ellen Pompeo. Pompeo recently announced that she’s expecting her first child.
“Grey’s Anatomy” airs its 100th episode Thursday, May 7.