The married mom of two enjoyed some fun the sun with fruity cocktails and close pals including Samantha Ronson (who also sported a two-piece) in Mexico Friday.
Clad in a tiny black bikini, the birthday girl flaunted her healthy figure but showed no sign of vegging out on the massive three-tier birthday cake at her A-list party two days prior, where she gathered a bevy of family and friends like her hubby Joel Madden, Ronson, Mary-Kate Olsen, Benji Madden and dad Lionel Richie at a deluxe suite at the Beverly Wilshire.
"I can't believe the outpour of birthday love I am getting on twitter today!" Richie wrote on her Twitter account September 21. "From the bottom of my heart (& the top), THANK YOU SO MUCH!"