The short answer is horribly, but okay, you might want more details than that.
Since his discovery in 1922, there have been numerous theories, some of which have been pretty outlandish.
X-rays conducted in the 1960s revealed a fragment of bone in his brain cavity, possible evidence of murder by bonk on the head, but closer examination showed that the sliver probably broke off after death.
In 2005, a broken leg and massive chest wounds led to the conclusion that not only had he fallen off a chariot while hunting but he also was run over by one.
DNA tests from 2010 point straight to malaria, which would have made his broken bones even worse.
And in 2013, a doctor examined CT scans and stated that the chest wounds actually came from the bite of - I swear I can't make this up - a hippopotamus.
So here's MY scenario: The unfortunate boy-king gets clocked in the head by a jealous rival while out hunting hippos by chariot. He tumbles off and is run over.
The hippo charges, and Tut manages to get up and run, but his club foot, broken leg and malaria slow him down. The hippo practically bites him in half...and then Tut spontaneously combusts.
Yes, the most recent speculation is that Tut spontaneously caught fire in his coffin.