Josh Brolin and Wife Kathryn Expecting Second Child Together: 'The Brolins Are a Growin'!'

Josh Brolin is about to become a father of four!

The actor's wife Kathryn spilled her pregnancy news on Instagram Tuesday, sharing a photo of herself posing outdoors with the couple's 20-month-old daughter Westlyn Reign.

As she and the toddler share a smooch, Kathryn, 32, bares her baby bump under a black crop top, finishing the look in a pair of denim shorts and a cowgirl hat.

"The Brolin's are a growin' !!" the entrepreneur captioned her post. "Our little December babe is on the way ...🌱"

Josh, 52, left a cheeky comment on the post, writing, "Wow. That's amazing! Congratula ... wait ... WHAT?!?!"

Plenty of the couple's famous friends chimed in as well, like Josh's Marvel costar Zoë Saldana, who remarked, "Biggest congratulations!" along with a string of clapping-hands emojis.

BACKGRID Kathryn Boyd, Josh Brolin

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RELATED: Barbra Streisand Shares Cute Sign Stepson Josh Brolin and Kathryn Boyd Made While Social Distancing

Josh and Kathryn announced Westlyn's birth in November 2018, with the actor sharing a video of his then-newborn baby girl fast asleep.

His father James Brolin spoke with PEOPLE Now in April of last year about his son's reaction to becoming a father again three decades after his first child was born, saying he "dropped everything" related to work and took on "nothing but diapers for three months," despite how busy he was.

And as for how his wife Barbra Streisand is as a grandma, "The minute the kid comes into the room, she just changes into another person. She falls apart," said James, 79. "And she's persnickety ... the minute the kid comes in, all that just goes out the window. It's really fabulous to see."

Aside from Westlyn, Josh has two adult children — daughter Eden, 26, and son Trevor, 32 — from his first marriage to actress Alice Adair. Josh and Kathryn tied the knot in September 2016.

View this post on Instagram

My people. 🌿

A post shared by k a t h r y n b r o l i n (@kathrynbrolin) on May 16, 2020 at 8:17pm PDT

RELATED VIDEO: James Brolin Says Son Josh "Dropped Everything" When His Daughter Was Born

James Brolin Says Son Josh 'Dropped Everything' When His Daughter Was Born

PLUS: What does James Brolin get wife Barbara Streisand for her birthday?!

Off the heels of his wildly successful run as supervillain Thanos in the Marvel Cinematic Universe, Josh — who made his big-screen debut as Brand in the 1985 adventure film The Goonies — is set to receive a star on the Hollywood Walk of Fame next year.

Other film honorees will include actors Zac Efron, Shia LaBeouf, Naomi Watts and Morris Chestnut — as well as Josh's fellow MCU stars Don Cheadle and Benedict Cumberbatch, according to Variety.

The original cast members of The Goonies, including Josh, recently reunited for a virtual reunion hosted by Josh Gad amid the novel coronavirus (COVID-19) global health crisis.

Gad, 39, was also joined by Sean Astin (Mikey), Corey Feldman (Mouth), Jeff Cohen (Chunk), Martha Plimpton (Stef), Jonathan Ke Quan (Data), Kerri Green (Andy), Robert Davi (Jake Fratelli) and Joe Pantoliano (Francis Fratelli). He even had special appearances from theme-song singer Cyndi Lauper, screenwriter Chris Columbus, executive producer Steven Spielberg and director Richard Donner.