Josh Brolin is to be a father for a third time.

The 50-year-old actor - who has two kids, Trevor, 29, and Eden, 24 from his previous marriage to Alice Adair - took to Instagram to reveal his 30-year-old wife Kathryn is expecting her first child, and the little one is currently ''no bigger than a sweet potato''.

He wrote: ''There's a new sheriff in town, and she's no bigger than a sweet potato. Hang on to your hats. #jbkbstucktogether #lilbeanterritory #loveisaslovedoes (sic)''

The 'Deadpool 2' star shared a picture of Kathryn showing off her baby bump in a crop top while on a walk.

She also took to her Instagram account to share the happy news by posting a picture of herself revealing her bump by lifting up her shirt.

Kathryn wrote: ''Something's cookin... Baby Girl Brolin on the way #jbkbstucktogether #loveisaslovedoes (sic)''

Josh married his former assistant Kathryn in September 2016 after he popped the question in March 2015.

The couple said their vows in an intimate ceremony in front of close family and friends in North Carolina.

Josh, Kathryn, and their guests shared photos from the big day and the run up to their nuptials on social media using the hashtag #JBKBStuckTogether.

Before the wedding, Josh admitted planning the ceremony had turned him into a ''control freak''.

He said: ''I'm the guy who has to force himself to back off!

''I'm such a control freak and I want to control everything. It's not even that I want to control it - I just want to be in the middle of it.

''I want to be in the nucleus of it because that's the fun part. That's the nectar.

''We're still in the midst of figuring out the best time and all that stuff, but it's very exciting.''