costume brentwood halloween Jessica Alba Cash Warren Leonardo DiCaprio

A certain hunky celeb wore one scary mask for Halloween!

The actor, 36, wore the mask at Kate Hudson's big Halloween bash over the weekend, where he snapped photos on his cell phone with friends.

A few hints to help you: 1) This critically acclaimed star was abroad and had to fly back to the U.S. for Hudson's soiree. ... and 2) Wearing a hoodie, as he did here, is nothing new for this hottie!