The couple, who have been married for nine years, announced the news on Instagram.
Posting an adorable pic of her newborn, Alba wrote: 'Hayes Alba Warren 12/31/17 Best gift to ring in the New Year!! Cash and I feel so blessed. Haven and Honor are already obsessed with their new baby bro. 👶🏽💙 #familyof5'
Alba and Warren also share two daughters, Haven Garner, 6 and Honor Marie, 9.
This article originally appeared on New Idea