LAS VEGAS -- Former UFC lightweight and welterweight champion BJ Penn retired from professional mixed martial arts at the age of 35 on Sunday.
Widely considered the best lightweight of all time, Penn announced his retirement following a third-round TKO loss to Frankie Edgar at "The Ultimate Fighter" finale.
Prior to the loss, Penn (16-10-2) had not fought since dropping a lopsided unanimous decision to Rory MacDonald in December 2012. The intrigue of a third fight with Edgar, whom he had twice lost to previously, talked Penn back into competition in 2014.
After losing to Edgar (17-4-1) for the third consecutive time, Penn said he knew it was time to hang up his gloves.
"This is the end," Penn said. "I'm thinking to myself, 'Why did you step back in the Octagon after the beating Rory MacDonald gave you?' The reason is I really needed to find out. If I didn't make this night happen, I would have always wondered.
"I would have complained to everyone, 'I could have done it again! I could have done it again!' Now, I know for sure that I can't."
Penn remains one of only two fighters in UFC history to win titles in multiple weight classes. He won the UFC 170-pound title by submitting Matt Hughes at UFC 46 in January 2004. Four years later, Penn added the 155-pound title to his résumé in a submission victory over Joe Stevenson at UFC 80. He defended that title three times.
"I guess now that I look back, my biggest accomplishment was the two belts in two weight classes," Penn said.
He fought former UFC welterweight champion Georges St-Pierre to a narrow split decision loss at UFC 58 in March 2006. He challenged St-Pierre a second time for the welterweight title in January 2009 and lost via TKO.
UFC president Dana White said, "He's one of the best 155-pounders of all time. He helped build that weight class and he was responsible for helping build the UFC. That's his legacy."
Sunday marked Penn's debut in the 145-pound featherweight division. His previous two losses to Edgar were competed at lightweight. In the third round, Edgar opened a cut near Penn's left eye with an elbow. He finished the bout minutes later via strikes on the ground.
"Definitely when the blood started going down into my eyes and the fight started to get real tough, I realized it takes a high, high level of energy to compete with the top people in the world," Penn said.
Penn had hinted at retirement after each of his prior two losses but stopped short of officially announcing the end of his career. In addition to wanting time off, Penn hadn't fought since December 2012 due to a necessary surgery on his left eye.
Ahead of the Edgar fight, White had stated he would urge Penn to retire if he didn't win, as he's done with other former champions. On Sunday, Penn said he agreed with White.
"I think it's never over for these guys," said Penn's older brother, J.D. "[Former UFC light heavyweight champion] Chuck Liddell and Matt Hughes came in the back after the loss and when you look at them -- when you're a real fighter, you never accept closure.
"When you have your family around, it helps you lean that way, but inside of those guys -- Matt and Chuck, any of those guys -- they are fighters. I don't think that ever ends."