Happy birthday, Jessica Simpson [1]! The singer turned fashion designer turned 39 on Wednesday, and she celebrated in one of the sexiest ways possible: in a leopard bikini! Jessica threw an over-the-top pool party with her closest friends, including CaCee Cobb and stylist Nicole Chavez. "39 is all mine!!!" she captioned a glamorous Instagram shot of herself [2] in jeweled sunglasses, gold hoop earrings, and a leopard beach cover-up.

Jessica's fun-filled bash comes just a day after she excitedly announced that she's releasing her first memoir [3], which hits shelves in February. "I have been working so hard on it," Jessica wrote on Instagram. "I have opened my heart up in a way I never have before and now I can't wait to share it with the world." In addition to her upcoming book, Jessica and husband Eric Johnson [4] welcomed their third child, a baby girl named Birdie, in March. Birdie now joins their two other adorable kids [5], 6-year-old son Ace and 7-year-old daughter Maxwell.