Kate Upton was upstaged by her own ass at her 24th bday party in NYC Wednesday night -- hitting up the bash with her MLB star fiance Justin Verlander in a see-through outfit.
The Detroit Tigers pitcher was all smiles as he walked Upton into the bash at The Blond lounge -- and it's obvious why.
Huge stars like Bella Hadid and Nick Jonas also hit up the party ... wearing WAY more clothes.
Cheers to the bday girl.
