One of the pics is of him sitting shirtless on the floor with his back against the side of a bed, wearing only some Calvin Klein boxer briefs with his legs spread seductively. In the second photo, he's showing off his abs again while looking like he doesn't totally understand how to actually take his t-shirt off.
The third photo is the most-clothed, in that he's wearing jeans and a denim over-shirt, but still shows off his abs with no undershirt, and his Calvin Klein boxer-briefs rising above his waist line, as he forgot to button his pants.
Despite (or perhaps due to) Mendes' apparent propensity for forgetting how to wear clothing, and his remarkably fit physique, some of the singer's famous friends and a slew of his biggest fans were coming out of the woodwork to fawn all over the 20-year-old heartthrob.
Demi Lovato was was one of the first to comment on Mendes' Instagram post, wordlessly reacting with three fire emojis -- presumably one for each pic.
For a look at some of the other hottest men in Hollywood who've been taking off their shirts and flaunting their impressive abs in recent weeks, click through the exhaustively researched gallery below.