It seems Riccardo Tisci can do no wrong. So after yet another stellar Givenchy collection yesterday, what else but throw a star-studded bash that doubled as a surprise birthday party for longtime muse and bestie of 15 years, Marciacarla Boscono? But this was no cake-and-balloon affair—well, it was, but reinvented in Givenchy black. The glamorous fete took place at L’Arc, fashion’s new hotspot near the Arc de Triomphe and the perfect backdrop for the Italian usurper who’s quickly become the toast of Paris.

The intimate soiree, which looked less like the usual stiff fashion party and more like an after-hours rager, drew Givenchy groupies from far and wide. Guests included Carine Roitfeld, looking fresh after her triumphant masked ball, Julia Restoin-Roitfield, and Justin Timberlake, who even brought along some of his Social Network pals.

Of course, no fashion fete would be complete without a surprise performance. This time it was the unsinkable Courtney Love, who wowed the crowd with a hearty cover of Bad Romance. You may not know it, but Love also has a soft spot, and she punctuated her set with two renditions of Happy Birthday for a very moved Boscono.