“We had a baby last night,” reads the caption. “He’s perfect and we couldn’t be happier. Watch for a name.”
“I love you, @hilariabaldwin,” he wrote. “My karma is your karma. Your karma is mine.”
Hilaria Baldwin, a fitness entrepreneur and co-host of the Mom Brain podcast, shared the news in April that she was pregnant after two abortions.
The couple is also Romeo’s parents at 2 years old; Leonardo, who turns 4 on Saturday; Raphael, 5; and Carmen, 7.
Alec Baldwin also shares his 24-year-old daughter Ireland with his ex-wife, actress Kim Basinger.