The former UFC heavyweight champion had the chance to reclaim his gold but came up well short, losing to current champ Junior dos Santos via second-round TKO.
Mir just wasn't able to fight his fight. He wanted to get things to the ground, and dos Santos would have none of it.
Forced to stand, Mir was trading with the best boxer the UFC heavyweight division has ever seen, and that generally doesn't work out too well.
He held on as long as he could, but dos Santos' power was too much for Mir, who was eventually rocked and finished with a flurry of punches and an emphatic hammer fist.
After his somewhat underwhelming performance at UFC 146, here are four questions we have about Frank Mir.
Was he in shape for the dos Santos fight?
Mir's cardio is always a question mark.
We saw him gas against Roy Nelson,and against dos Santos he seemed exhausted by the second round.
More than that, Mir looked a little chunkier than we're used to seeing him in the cage.
Given all that, it's hard to wonder if Mir was in the shape he need to be for this one.
Is his heart still in fighting?
I think it's fair to say that most wouldn't describe Mir's performance as motivated.
Indeed, halfway through Round 1, Mir seemed to have already abandoned his game plan and was content to play into dos Santos' strengths.
At 33 years old, having accomplished so much and being faced with the reality that's just not as good as the new breed of fighter, Mir doesn't seem to be the hungry fighter that he used to be.
How many fights does he have left?
Age 33 is not ancient for a heavyweight, but Mir has been in the sport for a long time and fought his share of battles.
It has been apparent over the past few years that Mir's body—his chin, especially—is starting to let him down.
In the heavyweight division, fighters need to be able to eat a good punch, and it's rare these days that we don't see Mir rocked in a fight.
He's one of the best ever and it will be sad to see him go, but you have to think that Mir doesn't have much more than two years left in him.
What does the future hold for Mir?
Mir is one of the smartest and most articulate fighters in MMA history. His ability to analyze fights and break down positions in a way that a general audience can understand is unrivaled.
After Mir retires, it would be a shame to see him just fade away from the sport.
Hopefully, once it comes time for him to call it quits, Mir will stick around as a guest—or possibly full-time—commentator and MMA analyst.
Andrew Barr is a Featured Columnist for Bleacher Report and a stand-up comedian. Check him out on Twitter @AndrewBarr8.