For those wondering about her pre-party routine, the new mom (who welcomed son Jack in August 2024) kicked off her birthday with what she called a “bday burn” workout session with trainer Kirsty Godson, proving that even birthday girls don’t skip leg day. Which, of course, makes plenty of sense when you’re going pants optional!

In lieu of a traditional going-out top, Bieber took a page out of Kendall Jenner's recent playbook by wearing her jacket as a shirt. However, unlike Jenner's tailored croc blazer, Bieber chose a thick (possibly faux) fur-lined jacket with a certain Death Becomes Her je ne sais quoi.