Brock Lesnar to UFC ... I'm Retiring from MMA

IT'S ALL OVER!!

Brock Lesnar has informed the UFC he's officially retiring from MMA.

The 39-year-old superstar informed the UFC about his decision, a rep for the organization tells MMAFighting.com.

Lesnar was a beast in his prime and beat up on some of the greatest fighters in UFC history -- including a win over Randy Couture to win the UFC Heavyweight title back in 2008.

Lesnar had been suspended for 1 year by USADA after failing two UFC 200 drug tests and would have been eligible to fight again in July. Instead, he's hangin' 'em up.

If Lesnar does decide to fight again, he would still have to serve the remainder of his suspension before he would be cleared to get back in the Octagon.

Back in August, Lesnar told TMZ Sports he was considering another fight ... but clearly, things have changed.