Conor McGregor has had enough.

The UFC star took to his Twitter account Tuesday afternoon to announce he's done with the Octagon for good and is retiring at just 27 years old.

I have decided to retire young.
Thanks for the cheese.
Catch ya's later.

— Conor McGregor (@TheNotoriousMMA) April 19, 2016

The shocking announcement comes just over a month removed from suffering a second-round defeat to Nate Diaz due to a rear-naked choke tap-out on March 5 in Las Vegas.

Let's just say Diaz isn't buying it, and he took to his own Twitter account to sarcastically respond to his rival.

I guess my work here is done I'm retiring too

— Nathan Diaz (@NateDiaz209) April 19, 2016

The two fighters were slated to have a rematch at UFC 200 on July 9, but this announcement seemingly ends any chance of that happening unless McGregor means he'll retire after facing Diaz for the second time in five months.

However, as ESPN.com points out, McGregor was deeply affected by something far more serious than losing to Diaz last month. Back in his hometown of Dublin, Ireland two weeks weeks ago, McGregor witnessed Portuguese mixed martial arts (MMA) fighter Joao Carvalho die from injuries suffered during his April 9 bout.

"To see a young man doing what he loves, competing for a chance at a better life and then to have it taken away is truly heartbreaking," McGregor wrote on his Facebook account last week. "We are just men and women doing something we love in the hope of a better life for ourselves and our families. Nobody involved in combat sports of any kind wants to see this. It is such a rare occurrence that I don't know how to take this."

He added: "Combat sport is a crazy game and with the recent incident in boxing and now this in MMA, it is a sad time to be a fighter and a fight fan. It is easy for those on the outside to criticize our way of living, but for the millions of people around the world who have had their lives, their health, their fitness and their mental strength all changed for the better through combat, this is truly a bitter pill to swallow. We have lost one of us."

Even after writing the emotional post, though, McGregor seemed hellbent on training hard for his rematch against Diaz. This Saturday, he posted "hungry like day 1" on his Facebook account, accompanied by a shot of him training. Then, yesterday, he added, "back in the land of Ice for some good training at Mjolnir!!"

So, this sudden tweet today definitely shocked. Twenty-seven is an early age to retire, but then again, Conor has some miles on him as a fighter.

Let's see if he keeps his vow or turns back on his tweet.