03/12/2009 AT 08:30 PM EDT
For Michael Phelps, what started as a night of celebrating with a small group in South Carolina turned into what he called "an awful judgment."
An email later alerted Phelps to the fact that an infamous photograph
of him holding a bong had started to surface, he tells Matt Lauer in a Today
interview airing Friday.
"I had no idea really what to do," he says. "You know, I knew that I'd made a mistake and made a bad judgment."
Lauer says to Phelps, "I have to ask you, were you smoking pot?"
Not directly answering the question, Phelps replies, "It was a bad mistake. I mean, we all know what, you know, what you and I are talking about. It's a stupid mistake. And it's something that, you know, I have to, and I want to teach other people not to make that mistake."
On Feb. 23, Richland County sheriff Leon Lott said that no charges would be filed
against Phelps or anyone present at the University of South Carolina party that November night due to lack of evidence.
The full interview also airs Sunday on NBC's Dateline