Josh Brolin and model Kathryn Boyd tied the knot in September 2016

Josh Brolin is thinking pink!

The actor and his wife, model Kathryn Boyd, are expecting their first child together, he announced Tuesday on Instagram.

“There’s a new sheriff in town and she’s no bigger than a sweet potato. Hang on to your hats,” Brolin captioned a photo series of the mom-to-be showing off her bare baby belly while out on a hike.

The Deadpool 2 star, 50, is already dad to two grown children, daughter Eden, 28, and son Trevor, 30 next month, from his first marriage.

Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.

Credit: Josh Brolin/Instagram

Brolin and Boyd, 31, who previously worked as the actor’s assistant, were spotted kissing while on vacation in Rome in February 2015.

RELATED VIDEO: Does Ryan Reynolds Take His Deadpool Suit into the Bedroom? He Answers People Readers’ Wildest Questions

After confirming their engagement that spring, the couple tied the knot during a September 2016 ceremony.

Brolin opened up about fatherhood on social media in April, sharing a photo of his two children in honor of Easter.

“There is no duo I love more than this punk rock duo, my two kids. They see the world through the ever revolving kaleidoscope it’s meant to be experienced through,” he wrote.

“I have been blessed with a potpourri of emotional fireworks because of them. And, over a quarter century into it, I am a better man because of them. I might not be as mature as they are, but there’s still time.”