The first play-off miss of his career and a torn ACL - it was a true nightmare for Patrick Mahomes and the Chiefs as their run of 10 straight post-seasons came to a shuddering end.
With nine straight division titles, seven straight AFC Championship games and five Super Bowls, three of them won, it's been an incredible run for Mahomes - who has never previously ended a season before overtime in the AFC title game.
And so the Chiefs' inquest begins, starting with questions of when Mahomes will be fit to return and whether 36-year-old tight end Travis Kelce or head coach Andy Reid, 67, will return at all amid retirement rumours.
But where did it all go wrong?
Firstly their big strength has become their biggest weakness - winning tight games. After an NFL-record 11 one-score wins last year, the Chiefs have won one and lost seven that way this season.
And everybody has been at fault, including Mahomes for throwing some costly red zone interceptions. Reid has made some bad calls and Kelce and his fellow receivers have literally dropped the ball.
Fatigue could be a factor. Since Mahomes became starter, the Chiefs have played just two games under the maximum, and the constant deep play-off runs and Super Bowls can take its toll.
The defence has been excellent again, but the offence has been guilty of making the wrong play at the wrong time.
The other main issue has been protecting Mahomes, with offensive line issues a theme over the past few seasons.
Mahomes has taken the most quarterback hits in the NFL this season with 65, has been forced to attempt the joint-most scrambles with 52 and been pressured the third-highest number of times with 135.
In short, Mahomes just hasn't had the protection, and even when he gets his throws off, he's had the second-highest number of dropped catches with 26. For his own part, he's second on the list for bad throws with 81.
The two-time league MVP is the best quarterback of his generation, but while he's made mistakes, the team just haven't helped him.
The Chiefs' main priority once he returns is to protect their star man better and give him more reliable pass catches to let him do what he does best.