And while we don't really think we have to explain why, we want to!!
The Cake starlet brought out a plunging black and lace vintage Galliano gown, which looked perfectly fitted to her svelte figure.
Of course, if the fit wasn't enough to get hearts racing, her neckline definitely did the job.
Sigh. Besides, she also paired her same bodychain from the Critics' Choice Movie Awards to accentuate her eye-popping cleavage, along with a collection of Fred Leighton jewels.
Oh, and Justin looked pretty amazing himself, complementing Jen in a classic black and white tux.
[Image via Getty Images.]