"Cheers to last rose & last huju," he wrote alongside a snapshot of the season 17 stars kissing and holding champagne. "Poppin bottles to new beginnings with @thekatiethurston!"
Blake then expressed his excitement over starting their "best f--king life" together and praised his fiancée.
"You're a rock. My rock. A mature, nurturing, supportive & loving partner who continues to impress me everyday," he continued. "We have an adventure called life ahead of us and I hope you know I'll do everything I can to help, push and encourage you to make the most of every little bit of it!"
He also revealed his nickname for Katie. "I love you buggy," the wildlife manager added. "Ya, that's my nick name for her. Buggy."
It turns out Katie has a nickname for her main man, as well, which she revealed in a birthday tribute to Blake.
"Happy f--king birthday honey bear!" she wrote in a separate Instagram post of the duo marking the occasion with party hats, cake and a smooch. "What a wild couple of months it has been. I couldn't have done this without you. I'm so ready to leave these bubbles and start living our life!"
The marketing manager then noted she "couldn't ask for a better partner" in life. "You are kind, patient, understanding, and your advocacy for the planet and animals is remarkable," she wrote. "I'm so lucky to call you my fiancé. My best friend. My confidant. We are just two weirdos laughing our way through life together. Cheers to the upcoming adventures! Next stop..CANADA!"
Blake, who previously appeared on Clare Crawley's and Tayshia Adams' seasons of The Bachelorette and joined Katie's late, was one of the final two suitors along with Justin Glaze after fellow contestant Greg Grippo left the show. But after Katie professed her love for Blake on their fantasy suite date, she knew he was the one and sent Justin home.
"I truly actually did not think he was going to propose," Katie told Good Morning America in an interview that aired Aug. 10. "And so then when he actually got down on one knee and proposed, my reaction is actual shock."
Now that her Bachelorette journey is over, Katie is looking forward to her next chapter with Blake. "At some point, there's certainly a wedding, " she said on GMA, "there's no doubt about that."