Blake, 31, was apparently shocked to find out Katie and John, whom the Season 17 The Bachelorette star eliminated during Week 2 of the show, are dating so quickly after she and Blake announced in late October they had ended their engagement and split.
Lyrics of "Begin Again" include, "I've been spending the last eight months / thinking all love ever does is break and burn and end / But on a Wednesday in a cafe, I watched it begin again."
Katie flashed those specific lyrics across a video of John and herself riding in a small plane together. She also showed a clip of a fancy cocktail she was sipping on while John, a 27-year-old bartender from Pacific Beach, CA, was working behind the bar.
"Yeah, that's my type," Katie told the cameras after John introduced himself on Night 1 during The Bachelorette's June premiere. "I think that's my type. Did he hear me? Play it cool."
Later that evening, Katie uploaded one of John's TikTok videos to her Instagram Stories that showed the couple walking arm-in-arm down a hallway and embracing and kissing.
While Blake has yet to put out an official statement regarding Katie and John's new relationship, Blake's mother Emily Moynes made her feelings known by "liking" a fan's comment slamming Katie's recent actions.
"In any relationship, you put a sense of 'trust' in one another, especially long-distance relationships. There's no denying the dishonesty and deception for months upon months."
Speculation Katie and John are dating have swirled for quite some time now, even though Katie had been engaged to Blake -- whom she dated for about six months -- prior to the big announcement of their split late last month.
This past summer, Katie posted footage of herself at a bar John works at in San Diego, which prompted rumors John may have been the winner of her The Bachelorette season.
However, The Bachelorette viewers saw Katie eliminate John during Week 2 of the process and eventually accept a marriage proposal from Blake on the Season 17 finale, which filmed in April and aired in August.
(Katie dedicated Day 1 of her "Messy" challenge to Blake by choosing "We Are Never Ever Getting Back Together" as his dedication).
Katie proceeded to move to San Diego and continue hanging out with John while Blake -- a wildlife manager who lives in Toronto, Canada -- 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.
A source told Us earlier this month that Katie has found "clarity" and now "knows what she wants in a husband" after her failed engagement to Blake.
But when Katie accepted Blake's marriage proposal on The Bachelorette, she seemed totally convinced that he was The One for her.
"I think everyone can agree that this is exactly who I was supposed to be with. He fought to be here for me and chose to stay even when I'm telling him to his face that I considered leaving," Katie said on The Bachelorette: After the Final Rose.
On November 1, Blake shared on Instagram how he had been relying on family, friends and his dogs to get him through his breakup with Katie.
"When times are really tough and things just aren't going the way you had hoped... it's always the same 'gang' that gets ya back on your feet," Blake wrote at the time. "Feels good to start getting back into the swing of things."
Reality Steve spoiler blogger Steve Carbone reported late last month that The Bachelor will be airing two seasons of the show, Season 26 -- starring Michelle Young's The Bachelorette suitor Clayton Echard -- and Season 27 in 2022.
According to the @Deuxmoi Instagram gossip account, ABC is considering Blake as the leading man for Season 27 due to his "really big personality" and similar The Bachelor franchise storyline to Nick Viall.
The Bachelor's 27th season is expected to begin filming in February 2022 and premiere in Spring 2022.