On Tuesday, the reality TV star shared a photograph of her and Barker holding hands with no caption.
Barker, who was not tagged in the post, commented below with a love heart emoji.
The 45-year-old musician also shared the post on his own Instagram Stories.
The revelation comes after Kardashian shared a photograph of a poem on Valentine’s Day in relation to her relationship with Barker.
“Roses are red, violets are blue, garlic bread, Blink-182,” read the note, which was shared on her Instagram story.
The couple have been photographed in public before, but this is the first time they have acknowledged their relationship on social media.
The post has already garnered more than 2.7m likes and thousands of comments from fans and friends, including one who wrote: “When friends become lovers”.
Another teased: “Please get married and have a goth wedding.”
“What a match made in heaven!” one fan commented. “Two super nice people who both deserve a super nice relationship! Happy for y’all!”
Others already labelled the relationship, ending their comments with the hashtag “#Kravis”.
Kardashian has three children with her ex and co-star on Keeping Up With The Kardashians, Scott Disick: Mason, 11, Penelope, eight, and Reign, six.
Barker also has three children with his ex wife, Shanna Moakler: Atiana, 21, Landon, 17, and Alabama, 15.
Barker has previously spoken about his friendship with Kardashian, tellingPeople in 2019: “Kourtney’s like a dear friend. That’s it… I mean, I love her to death. I love her family to death. But yeah, just friends.”
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