The reality queen turned heads on her big 4-4 Monday, rocking her eye-popping curves in a tiny silver bikini on the set of a top-secret filming project in Malibu -- making sure to steal the spotlight from her family, who were also there as the cameras rolled.

Kim looked absolutely stunning, raising temperatures in a sarong cover-up that wasn’t doing much to obscure that iconic bum.

Billionaire Kim was in her element, soaking up the autumn sun and radiating happiness as she filmed alongside her momager Kris Jenner and her man, Corey Gamble.

Cameras were also rolling on Kim's sisters Kourtney, Khloe and Kendall -- as well as some of the Kardashian kids, including Kim's children Saint and Chicago -- making it one heck of a family affair.

Of course, for the Kardashian crew, being in front of the camera is like breathing! So you know workaholic Kim wasn’t about to kick back and take a day off on her birthday -- she’s all about that hustle, even while celebrating. Happy birthday Kim!!!