Daniel Cormier declared it has "been a helluva ride" and paid tribute to victorious opponent Stipe Miocic in a farewell message to UFC.
The legendary Cormier took heavyweight champion Miocic the distance in Saturday's trilogy bout in Las Vegas at UFC 252 but suffered a unanimous decision defeat.
Cormier, who said his vision was impaired by a poke to the eye in the third round, insisted prior to the showdown the fight would be his last, a message he reiterated after his loss.
UFC president Dana White said he doubted the 41-year-old – a former champion in the light heavyweight and heavyweight divisions – would stay retired.
But Cormier is still sticking with his decision, writing on Twitter: "Thank you all for the love and support. Not what I wanted or expected but it is what it is.
Thank you !! pic.twitter.com/7VSVSn3Dra— Daniel Cormier (@dc_mma) August 17, 2020
"Congrats to @stipemiocic on a fantastic fight, was an honour and pleasure to share the octagon with you for 50 minutes. Boy did we give 'em a show every time.
"To my team: I love you all to death, you've made so many sacrifices. I hope I made you guys proud. Salina and the kids: thank you for being my motivation. To all the fans: I love you so much. You guys push me to try and be great.
"To @danawhite and the @ufc: I have loved every minute. Thank you for giving me the opportunity. Been a helluva ride, huh?"