“Trump has a big red yuck on his neck,” Kimmel said, referring to a large rash-like patch of skin that recently appeared around the president’s collar.

The White House has said it was due to the use of “a very common cream” prescribed by his doctor as a “preventative skin treatment” and that the redness was expected to last a few weeks.

President Donald Trump appeared to have a rash on his neck as he awarded the Medal of Honor to three U.S. Army soldiers on Monday.

Jim Lo Scalzo/EPA/Bloomberg via Getty Images

But Kimmel had his own theories about the rash.

“Just when you thought Melania couldn’t find another reason not to sleep with him,” he cracked. “Or maybe she tried to strangle him in his sleep. I don’t know.”

To get to the bottom of the mystery, Kimmel brought in a surprise guest: the red mark on Trump’s hand.

Check it out in his Wednesday night monologue: