A source tells ET, "Kourtney and Travis have had a platonic relationship for years and they’ve been friends and family friends for a very long time, but recently something sparked and their relationship has turned romantic."
"They live on the same block and things are super easy between them because they know each other so well and just click and get one another," the source adds. "Her kids and his kids get along so well too, which is a major plus for both of them."
Kardashian, 41, and Barker, 45, first alerted fans to their possible relationship over the weekend, as they appeared to be spending some quality time together at Kris Jenner's home in Palm Springs, California. The pair both shared poolside views of the backyard.
Barker is dad to 17-year-old son Landon and 15-year-old daughter Alabama, whom he shares with ex-wife Shanna Moakler.
Kardashian, meanwhile, is mom to 11-year-old son Mason, 8-year-old daughter Penelope and 6-year-old son Reign, whom she shares with ex Scott Disick. Though Kardashian and Disick ended their nine-year relationship in July 2015, they've worked together to co-parent their kids -- and occasionally keep fans guessing about the status of their relationship with flirty comments on Instagram.
Last month, Disick praised Kardashian, writing in a family photo on Instagram, "Thank you @kourtneykardash for being the best baby maker in town, I couldn’t have asked for a better person in the world to have these amazing children with, I love u and our family more than anything in the world 🌎."