John posted a photo of the couple kissing under a mistletoe in December 2021 when they had attended a Christmas ball in San Diego, CA.
"I could have never dreamt up what this year had in store for me," John captioned the picture.
"I am both in awe of, and extremely grateful for the circumstances that brought us together. And thank goodness you dumped me on national television, or else we could have never gotten to where we are now."
Katie and John went Instagram official with their relationship on November 23, only three short weeks after Katie and her former fiance Blake Moynes -- who won The Bachelorette's seventeenth season -- announced in late October they had split and decided to end their engagement.
"Falling for you was the best decision I never had a say in," John continued in his post, "and I couldn't be happier."
"Cheers to another year around the sun -- happy birthday beautiful girl!!" he concluded.
Katie commented on the touching post, "I sure do love you," along with a red heart emoji.
Based on Katie's Instagram Story, she and John are celebrating her birthday in Cabo San Lucas, Mexico. Katie has been spoiled with balloons, meals in bed and a beautiful view from her hotel room.
Katie and John also apparently enjoyed a fun night out at a local bar called Saloon Cabo.
Katie unveiled John as her new boyfriend late last year by posting footage of John on her Instagram Story set to Taylor Swift's "Begin Again," a song about falling in love all over again.
The John dedication served as the conclusion of Katie's "12 Days of Messy" challenge in which she had been tasked with matching every song on Taylor's re-released "Red" album to one of her Season 17 bachelors.
Katie subsequently faced backlash for moving on from Blake too quickly with a "rebound," and many The Bachelorette fans were upset with Katie for not warning Blake about her new relationship before telling the world about it.
Blake admitted in a November appearance on the "Talking It Out with Bachelor Nation" podcast that he had been "flabbergasted," shocked and "speechless" to learn about Katie's romance with John.
Blake also believed Katie must have been emotionally cheating on him with John in order to have moved on so quickly from their relationship.
"We talked about giving Blake a heads up. [But] here's the thing that people, I think, forget: We're just normal people trying to live normal lives," Katie said in an Instagram Live session last month, according to E! News.
"And when have you ever had to tell an ex that you're seeing someone new? And like, how would you tell them that? And would I still have received the same amount of hate even if I did give Blake a heads up? I don't know."
Katie also shared with her fans at the time how she's "the happiest" she's ever been.
"I wanted to make a big, grand statement about where I'm at and who I'm with and that's all I can do is live my truth, live my happiness," Katie reportedly explained.
She added, "I wanted to really show that, to me, John is my world. John is handsome. John is romantic. John is everything... Was there a lot of hate that came with it? Yeah."
Although Katie never let Blake down gently in regards to her seemingly-sudden feelings for John, she told Us Weekly on its "Here for the Right Reasons" podcast in December that she had spoken to Blake recently.
When asked if she had talked to Blake at all, Katie replied, "Yes, yes."
"I'll leave it at that," Katie noted at the time.
Katie accepted Blake's marriage proposal when The Bachelorette's Season 17 finale filmed in April 2021, but the former couple's engagement didn't air until August on ABC.
In defense of her connection with John and why she had dumped him so quickly on The Bachelorette, Katie shared with an Instagram user last month, "It would have never worked for us on the show. He was too shy. A solid friendship first built an amazing foundation."
Katie previously hinted on social media that she and Blake had been fighting too much during their six-month relationship and decided to break up due to their different communication styles.
John also recently posted a lengthy statement on Reddit to set the record straight on the circumstances in which he and Katie began dating.
"Katie and I developed an incredible and deep friendship over the last half year or so. The circumstances by which this friendship formed was a series of crazy, random, and coincidental events," John wrote late last year.
"My point for now, is that we were ALWAYS platonic," he clarified. "Even during my short stint on the season, we never had a chance to foster anything romantic (read as: John blew his chance and left the next day hahaha)."
John suggested that he had nothing but respect for Katie and Blake's relationship while they were together for six months.
"It was never a thought in our minds that we would ever be anything more. You guys -- she was engaged," John explained, adding, "Neither Katie nor I would ever cheat, push someone to cheat, or be involved in cheating."
John insisted being unfaithful to a partner "is not acceptable" and "not okay."
"Maybe this message deserves its own paragraph: There was no wrongdoing prior to the end of their engagement," John claimed.
"Furthermore, I understand that the timeline seems fast and messy. But I urge you to put yourselves in our shoes. Once Katie and I realized there was a romantic connection that we were interested in exploring, we were not starting from scratch; we were building off of the foundation of a close friendship through which, we had already gotten to know each other so well."
John apparently fell for Katie hard and fast once romance actually became an option for them.
"The speed at which I fell for this incredible, nurturing, and genuinely caring human being was honestly terrifying. I was scared. But every step of the way felt so right," John shared.
John said he had simply fallen "helplessly" for his best friend and there was nothing secretive or scandalous about it, except for the way fans may have perceived the situation.
"As I mentioned before, cheating in any form is unacceptable, and I'm sorry if it looked as though either of us were taking advantage of anyone's trust," John concluded.
Speculation Katie and John are dating began swirling in Summer 2021, when Katie posted footage of herself at a bar John works at in San Diego, which prompted rumors John may have been the winner of herThe Bachelorette season.
Katie proceeded to move to San Diego and continue hanging out with John while Blake traveled to Africa to pursue his wildlife conservation efforts.
Katie and Blake attempted to make a long-distance relationship work as people simultaneously questioned if sparks were flying between Katie and John.
"Internet rumors lead me to this guy becoming a dear dear friend," Katie reportedly wrote on Instagram in September after enjoying a day out with John in California.
While Katie was trying to mend her broken heart in late October, she uploaded a photo of John's dog to her Instagram Story and wrote, "Dexter forcing me out of the house this morning."
Katie had addressed the John dating rumors in early November but danced around an official confirmation or denial.
At the time, Katie shared a throwback video of "the first time I saw John since filming" on her Instagram Story that showed Polaroid photos of the supposed close pals playing cards together, Us reported.
"Y'all getting wild in my DMs," Katie wrote along with a laughing emoticon on November 7.
Blake told The Bachelorette alums Bryan Abasolo and Mike Johnson on "Talking It Out" that even if his split from Katie was "mutual," now he wonders if John was "always in her back pocket" and Katie's "Plan B" based on the timeline.
Another reason Katie and Blake may have broken up? An insider told The Sun that Katie's "outbursts eventually became too much" for Blake "to handle" during their relationship.