Olympic great Michael Phelps acknowledged “regrettable” behavior and “bad judgment” after a photo in a British newspaper Sunday showed him inhaling from a marijuana pipe.

In a statement to The Associated Press, the swimmer who won a record eight gold medals at the Beijing Games did not dispute the authenticity of the exclusive picture published Sunday by the tabloid News of the World.

“I engaged in behavior which was regrettable and demonstrated bad judgment,” Phelps said in the statement released by one of his agents. “I’m 23 years old and despite the successes I’ve had in the pool, I acted in a youthful and inappropriate way, not in a manner people have come to expect from me. For this, I am sorry. I promise my fans and the public it will not happen again.”

News of the World said the picture was taken during a November house party while Phelps was visiting the University of South Carolina. During that trip, he attended one of the school’s football games and received a big ovation when introduced to the crowd.

While the newspaper did not specifically allege that Phelps was smoking pot, it did say the water pipe is generally used for that purpose and anonymously quoted a partygoer who said the Olympic champion was “out of control from the moment he got there.”

The party occurred nearly three months after the Olympics while Phelps was taking a long break from training, and his actions should have no impact on the eight golds he won at Beijing. He has never tested positive for banned substances. The case is unlikely to fall under any doping rules.

The USOC noted that Phelps acknowledged his mistake and apologized.

“We are confident that, going forward, Michael will consistently set the type of example we all expect from a great Olympic champion,” the group said.