While the reality star didn't caption the pic, many fans recognized Barker’s heavily tattooed hand from the sweet snap — and Barker commented a black heart emoji.
The drummer also shared the pic to his Instagram Story.
Fans and famous pals rushed to the comments to gush about the new couple.
"THIS," Addison Rae commented.
"Love you," Sophia Hutchins wrote.
"Yesssssssss ❤️," Olivia Pierson said.
The pair spent Valentine’s Day together when they both posted a photo of the same fireplace on their Instagram Stories. Barker also showed off a gold ankle bracelet, which may have been the 41-year-old’s gift. Meanwhile, Kardashian shared a poem that was a nod to the Blink-182 drummer. "Roses are red, violets are blue, garlic bread, Blink-182," the brunette beauty shared.
The two have been friends since before Keeping up with the Kardashians aired, but recently the friendship blossomed into something more, and they both happen to live in the same gated Calabasas community.
Barker and Kardashian previously sparked romance rumors when they were spotted having dinner in Malibu in 2019 and seen leaving a restaurant together in Los Angeles in 2018.
"Kourtney's like a dear friend. That's it," Barker said in 2019. "I mean, I love her to death. I love her family to death. But yeah, just friends."
Rumors swirled again in January when the pair went to Palm Springs, Calif.— where Kris Jenner has a home — for a weekend.
As for why they didn't take things to the next level sooner? "It never felt right for them to date or hook up until now, mainly because they were scared it might mess up their friendship," an insider exclusively told OK!. "But the chemistry has always been there. And finally, they've decided to give this a go, have as much fun as possible and see where it takes them."
When it comes to Kardashian's ex-boyfriend Scott Disick, "He's cautiously pleased to see her happy," said the insider, noting that he's "keeping a close eye on the situation," as any protective father would do.
But at the end of the day, added the insider, "Scott's in no position to be prying on Kourtney's life or trying to preach about who she gets to date."
Barker was married to Shanna Moakler from 2004-2008 and shares Alabama, 15, Landon, 17, and 21-year-old stepdaughter Atiana with the model.
Meanwhile, Disick is dating 19-year-old Amelia Gray Hamlin.