Read Joanna Gaines' sweet, supportive note to Chip ahead of his first marathon

This Sunday, "Fixer Upper" star Chip Gaines will run his first ever marathon, in what will probably be more of an adrenaline-filled moment than any Demo Day he's ever experienced (and that's saying a lot).

His wife and co-star, Joanna Gaines — who's carrying the couple's fifth child! — is already cheering him on, posting a sweet and supportive message on Instagram Friday night.

"I am thankful for your big heart and big vision," she captioned a photo of Chip running down a wide, empty road. "Go get 'em this weekend, and you better believe I'll be the first in line at the finish to give you the biggest hug!"

Joanna also recapped the story behind the inaugural Silo District Marathon, which the Gaineses are hosting in their hometown of Waco, Texas.

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Running a marathon was a goal Chip first considered while writing his book, "Capital Gaines," according to Joanna's post. But the idea was taken a step further when he met Gabriele Grunewald (Gabe for short) in New York City last fall.

Grunewald, a professional runner who's been fighting a rare cancer since 2009, inspired Chip, who explained in a January blog post that, after meeting her, he didn't want to spend another second standing on the sidelines.

"Given what she's gone through, I didn't have any excuse not to give this a shot," he wrote. "So I committed."

Grunewald has been helping Chip train from her home state of Minnesota. He's also been getting lots of support and messages of encouragement from his four kids.

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All of the profits from the marathon will go toward the Brave Like Gabe Foundation, which aims to help further research on rare cancers like Gabe's.

Joanna added in her post that 6,000 runners from seven countries and all 50 states will participate in the event that will include a full marathon, a half marathon and a 5K.

She ended her Instagram message with hashtag #yourbiggestfan.

Even though Joanna won't be running the marathon, Chip has found ways to cheer her on, too. He was spotted in the TODAY plaza holding a sign that read "I [heart] Joanna Gaines!" while she was discussing her new cookbook on the show.

Good luck, Chip! We're all rooting for you!