The 35-year-old Transformers actress and the 42-year-old Keeping Up With The Kardashians star were photographed being the ultimate fangirls together during Machine Gun Kelly's secret show on a rooftop in Venice on Saturday.
The ladies have been spending a lot of quality time together, thanks to their boyfriends.
Of course, Fox has been dating MGK for the past year.
As for Kourtney, she's not hiding her PDA-filled romance with Blink 182 rocker Travis Barker.
Travis plays drums for MGK, so all four were at the show, and Fox and Kourtney were there for support.
The actress showed up to the secret concert with her 31-year-old rapper beau and his 11-year-old daughter, Casie Colson Baker.
Wearing loose-fit distressed denim, Fox wore a flesh-colored push-up bra and wore a trenchcoat to complete the look.
Slipping into a pair of sparkling platform heels, the brunette bombshell accessorized with a tiger print bag.
Holding hands with her rocker boyfriend, MGK kept a tight grip on his daughter as the trio made their way past nearby photographers and into the show.
Once inside, MGK joined Travis on the stage while Fox made her way over to Kourtney and the KUWTK star's bestie, TikToker Addison Rae.
Fox and Kourtney were spotted sitting together and chatting it up during the concert.
The ladies seemed to be the best of friends and were photographed laughing and bonding while cheering on their boyfriends.
Fox -- who's never one to shy away from fangirling to the My Bloody Valentine's rapper -- was caught bobbing her head and singing along to the music in the VIP area.
Besides Kourtney and Addison, other stars at the show included Avril Lavigne's boyfriend ModSun, and Travis' two children -- 17-year-old son Landon and 15-year-old daughter Alabama.
Kourtney has been spending a lot of time with the Blink 182 drummer's kids, despite all the drama surrounding his ex-wife Shanna Moakler.
As Radar reported, Moakler went on a tirade, claiming Kourtney's sister Kim had an affair with Travis and broke up their marriage.
Landon and Alabama seemingly took Kourtney's side and she's been playing stepmom ever since, even taking them to Disneyland with her three children.
While Travis' kids and MGK's daughter were at the show, Megan Fox's three boys with her ex Brian Austin Green were nowhere in sight.