Liam Payne's former girlfriend Kate Cassidy is heating up the California desert ... spilling out of her outfit on Coachella Day 1.

Check out her sizzling Instagram post -- she's all done up, wearing a leather and denim miniskirt-and-tank set that barely holds in her voluptuous chest.

She doesn't seem to mind the tight squeeze ... playfully posing for the camera on the infamous Coachella Festival grounds.

As you know, Kate and the late One Direction star dated for about 2 years up until he suddenly died in Argentina in 2024 ... and, she actually spent 2 weeks with Liam in the South American country before she returned home prior to his passing.

She has continued posting tributes to him on her socials while opening up about her grief and finding the grounding to date again.

Liam actually attended Coachella back in 2019 ... though he never had the opportunity to grace the stage.