Spanish-born Hilaria, 33, took to Instagram to share the exciting news.
'Our Baldwinitos are getting a new teammate this spring. I’m gonna make them a special cake to tell them if it’s a boy or a girl,' she captioned a picture of herself and Alec, 59 playing with their three children, Carmen, aged four, Rafael, aged two and Leonardo, aged one.
Alec also has daughter Ireland, 22, with ex-wife Kim Basinger.