The couples were seated next to each other at the event on Saturday.
UFC 260 was a star-studded affair on Saturday night. Kourtney Kardashian and Megan Fox were both seen at the event in Las Vegas with their respective boyfriends, Travis Barker and Machine Gun Kelly, as they watched Francis Ngannou defeat Stipe Miocic.
Fox, 34, and Kelly, 30, made playful faces as they were spotted by cameras in the VIP section at the UFC Apex. They were seated next to Kardashian, 41, and Barker, 45, who color coordinated in edgy black ensembles, and looked quite cozy together.
"Kourtney Kardashian, Travis Barker, Megan Fox and MGK have had double date nights many times and are all good friends," a source tells ET. "They have a great time when they hang out as couples and it's very natural, easy and fun. They all have lot of shared interests like music, self-care practices and more. Kourtney and Travis are super into each other and Megan and Machine Gun Kelly are so in love. So it's nice for both couples to spend time with like-minded people."
Barker and Kelly have known each other for years, having collaborated on several projects. They most recently worked together on MGK's album, Tickets to My Downfall.
Kelly and Fox -- who was featured on his track, "Banyan Tree" -- started dating after meeting last year on the set of their upcoming movie, Midnight in the Switchgrass.
Barker and Kardashian, meanwhile, have been dating for a few months, after turning their longtime friendship into something more.
"Kourtney and Travis are in total lust over each other and she doesn’t regret going public with their relationship at all," a source told ET earlier this month.
"The relationship was a long time coming because the attraction has always been there on both sides," the source added. "They love the fact that they have a true friendship and bonded that way before taking anything further and making things romantic."