King Ryan shared the news in a lengthy social media rant on Wednesday ... in which he referenced his current performance-enhancing drug scandal, his mother's health, a lawsuit from Logan Paul's Prime drink company and his divorce from Drea Celina.

Garcia's claim comes on the heels of his massive win over previously undefeated Devin Haney in April ... which is now under review after his samples were popped for Ostarine, a banned substance.

While Garcia's team has maintained he unknowingly took the drug ... he could face a fine, suspension or even have his win over Haney stripped from his record altogether.

"Boxing will be alright without me," 24-1 Garcia said minutes ago on X. "But still sucks I was fun in the game. And it was fun to punch people."

Garcia said it won't be the last we see of him, though ... explaining he'll still train and may even dabble in music or acting -- but said the sport of boxing is too "corrupt" for his liking.

"The sad part is I’m a great boxer," he added. "And I entertain and knock people out. I’m sad bc I 💙 boxing. Praying for everyone and I hope everyone has a great life."

He ended his rant by proclaiming "I’m officially retired" ... and hasn't posted since.

The announcement is being met with a ton of skepticism, as Garcia openly admitted to trolling his social media followers with constant bizarre tweets leading up to the Haney fight.