Michael Phelps has issued a public apology after a newspaper published a photo of him apparently using illegal drugs.
Phelps, 23, who won eight gold medals at the Beijing Olympics last year, was pictured by the News of the World inhaling from a glass pipe.
Phelps issued a statement apologising for his 'regrettable' behaviour and for having 'demonstrated bad judgment'.
The statement read: "I engaged in behaviour which was regrettable and demonstrated bad judgment."
"I'm 23 years old and, despite the successes I have had in the pool, I acted in a youthful and inappropriate way, not in a manner that people have come to expect from me."
"For this, I am sorry."
"I promise my fans and the public it will not happen again."
The United States Olympic Committee (USOC), which last month named Phelps its sportsman of the year for 2008, admitted they were disappointed in Phelps.
"We are disappointed in the behaviour recently exhibited by Michael Phelps," the statement read.
"Michael is a role model and he is well aware of the responsibilities and accountability that come with setting a positive example for others, particularly young people."
"In this instance, regrettably, he failed to fulfil those responsibilities."
"Michael has acknowledged that he made a mistake and apologised for his actions."
"We are confident that, going forward, Michael will consistently set the type of example we all expect from a great Olympic champion."
The photograph is said to have been taken at a party at the University of South Carolina in November.