Kellan Lutz Flashes His Undies

Courtesy: Calvin Klein

Kellan Lutz is making us green with envy in this new sizzling underwear ad for Calvin Klein.

Lutz is part of CK's new X campaign featuring four hot men wearing tight underwear representing the four elements ... earth, water, wind and fire.

Our favorite Twilight hunk, who is representing "earth," is clearly one of the hottest guys on the planet!

See all four sexy Calvin Klein campaign photos in the gallery below.