The picture shows a closeup of Kardashian and Barker holding hands while in a car. Kardashian sports long nails with red tips, while Barker's tattoos are on display.
Barker commented with a black heart emoji and re-posted the photo on his Instagram Stories.
Kardashian's friend Khadijah Haqq showed her support for the couple in the comments.
"When friends become lovers," she wrote, adding a heart emoji.
Kardashian and Barker are longtime friends who were first reported to be dating in January.
"Kourtney and Travis are officially a couple," a source told Us Weekly.
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"They have been close friends for years and have been dating for a couple months. Travis is very smitten with Kourtney and has been for a while."
Kardashian and Barker spent Valentine's Day together Sunday. The couple both shared a photo on Instagram Stories of a crackling fireplace.
Kardashian has three children, daughter Penelope, 8, and sons Mason, 11, and Reign, 6, with her ex-partner Scott Disick, while Barker has a son, Landon, 17, and a daughter, Alabama, 15, with his ex-wife Shanna Moakler.
"Her family and friends all really like him. Their kids all get along too, which is sweet," a source told People.
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