The two 'Hills' stars shared the same space Friday on Kaitlynn's Instagram story, where Brody made a brief appearance as he playfully flipped her off and then pushed away her camera. She captioned the clip, "@brodyjenner single and chic!!" The vid has no sound.

It should be noted, Kaitlynn goes out of her way to call Brody "single" ... which backs up our earlier reporting that there was no real chance of a romantic rekindling between them.

It appears Kaitlynn ran into her ex during a little getaway in Malibu -- where she's been hiking and lounging ... and also grabbing dinner with his mom, Linda Thompson.

Kaitlynn posted a photo of her and her former sorta-mother-in-law breaking bread at Nobu, with another friend in tow. She captioned the pic, "feelin’ super lucky to be part of this modern fam." We know Kaitlynn and Linda have remained close -- they were seen embracing each other at a Halloween party last year. Clearly, KC's on good terms with 'em.

As we reported ... Kaitlyn and Brody called it quits earlier in 2019 after Brody supposedly refused to give Kaitlynn two things she'd been asking for ... a baby and a legal marriage. They had a wedding ceremony in Indonesia, but never legally got hitched.

Then came Miley Cyrus, who had a brief fling with Kaitlynn herself shortly after Brody and KC were over. That relationship fizzled out though, and Miley's been hanging with Cody Simpson since.