'Little People, Big World' 's Jacob Roloff Is Engaged!

Little People, Big World‘s Matt and Amy Roloff are going to be parents-in-law — again!

The former couple‘s youngest child, son Jacob Roloff, is engaged to his girlfriend, Isabel Sofia, he announced on Instagram Saturday.

“We got ENGAGED! It happened in Iceland on the frozen pond, Tjörnin, late on Christmas 🎄” Jacob, 21, captioned an engagement photo — captured by Monique Serra — of the couple. “So much love for this beautiful soul @izzysofia_ . Here’s to many more Christmas’, you n me.”

“Excited for a lifetime filled with travel, growing together and trying new things with you @izzysofia_,” he wrote in another post.

Isabel also shared the exciting news on her Instagram account: “We are finally ready to share with everyone… WE ARE ENGAGED!!! 😍💍”

Family matriarch Amy also shared her excitement — and stamp of approval — about the engagement in a loving post.

“And this happened! I couldn’t be a happier mom! My youngest- Jacob and the beautiful Isabel are engaged,” wrote Amy. “Love them both and excited to see where life will take them in their marriage! 💙💗 #amyssecondactcontinues #engagedtomarry #forthroloffwedding #love #wonderfultogether.”

In celebration of his birthday, Isabel dedicated a heartfelt birthday tribute to her fiancé on Jan. 17 and posted a throwback photo of the first image they ever took together.

“Our first ever picture together at Crater Lake 👉🏻 On our cross country road trip 👉🏻 Our trip to Iceland 😍 Happy 21st birthday to my very best friend, adventure buddy and partner in crime,” wrote Isabel. “Jacob, I mean… look how far we’ve come and how many places we’ve seen together. You’re such a dream, such a dream come true. There aren’t enough hours in the day to tell you how much I love you. Thank you for being you. Today we all celebrated you! And I will continue to every day for as long as I’m kickin’ ❤❤”

WATCH: What Was Little People, Big World’s Zach Roloff Most Nervous about on His Wedding Day?

Jacob’s engagement comes five months after his big sister, Molly Roloff, tied the knot with Joel Silvius in an intimate ceremony in August.

Both of his twin brothers, Jeremy and Zach, are also married and became parents within the past year. Zach and wife Tori Roloff welcomed son Jackson in May, and Jeremy and Audrey Roloff welcomed daughter Ember in September.