Nicole Auerbach, USA TODAY Sports

Olympic champion swimmer Michael Phelps was arrested for driving while under the influence early Tuesday morning, according to police.

Phelps, 29, also was charged with excessive speed and crossing double lane lines within the Fort McHenry Tunnel on I-95 in Baltimore, the Maryland Transportation Authority Police said. Police say he was driving 84 mph in a 45-mph zone.

According to the police statement, an officer spotted a 2014 white Land Rover speeding and followed it through the tunnel at about 1:40 a.m. The officer stopped the car just beyond the toll plaza, identified Phelps as the driver by his license and noted that the 18-time gold medalist "appeared to be under the influence."

"He was unable to perform satisfactorily a series of standard field sobriety tests," the police statement said.

Phelps was cooperative throughout the process, police said. He was later released.

"Earlier this morning, I was arrested and charged with DUI, excessive speeding and crossing double lane lines," Phelps said in a statement. "I understand the severity of my actions and take full responsibility. I know these words may not mean much right now but I am deeply sorry to everyone I have let down."

Phelps is the most decorated Olympian in history, with 22 medals from the 2004, 2008 and 2012 Olympics. He retired after the London Games, where he won four golds, but began training last fall and officially returned to competition in April. One of the reasons he returned to swimming, Phelps said this summer, was because it gave him a structured schedule. He repeatedly said he was bored in retirement.

"It's good to have some structure back in my life," Phelps said in July. "That's how I've always been. That's something I need. I was happy to get that year and a half where I did whatever I wanted, went wherever I wanted. I got that out of the way, and I'm happy to have this back."

Unlike 2008 and 2012, where he swam a full program, he has concentrated on relays and shorter-distance events in his comeback, including his signature 100-meter butterfly. At last month's Pan Pacific Championships, his first international meet since London, he won three gold medals and two silvers.

Phelps doesn't have any more meets scheduled this year so it's unclear what, if any, discipline he might face.

"The news regarding Michael Phelps and his actions are disappointing and unquestionably serious," USA Swimming said in a statement. "We expect our athletes to conduct themselves responsibly in and out of the pool."

U.S. Olympic Committee CEO Scott Blackmun said in a statement that he was "surprised by today's news" and "disappointed on a number of fronts," but would defer to Phelps and USA Swimming before saying more.

A spokeswoman for Aqua Sphere, which signed Phelps to a multiyear swimwear deal earlier this year, did not return an email seeking comment. Nor did Under Armour, another Phelps sponsor.

This is not Phelps' first brush with the law. In 2004, a 19-year-old Phelps was arrested for drunken driving and was ultimately sentenced to 18 months probation. In 2009, a photo surfaced of Phelps with a marijuana pipe at a party. He was suspended from competition for three months by USA Swimming, but was not charged with a crime.

Phelps received a probation before judgment disposition in 2004 — when he pleaded guilty to driving while impaired — so a judge might take that into consideration for his second DUI-related arrest.

"He served 18 months of probation, so I assume the charge was dismissed at that point so he doesn't have any conviction on his record, " said David Gray, a professor at the Francis King Carey School of Law at the University of Maryland. "Under the statute, this would be (viewed as) a first offense."

The penalties associated with a DUI (first offense) are up to one year in jail and/or a $1,000 fine. So while the prior arrest would likely not enhance the maximum penalty, it could come into play during sentencing.

"The fact that he doesn't have a prior conviction for a DUI doesn't mean he doesn't have a prior incident," Gray said. "A judge in this case, I think, would be more inclined to deal with this more seriously than he might if this was truly a first incident. Even though it's his first offense and he'd be governed by the maximum penalty of a year in jail or $1,000 fine, the chances are much higher that he would face jail time (in sentencing) because he has the prior charge."

Gray said another possible outcome is Phelps pleading out and accepting the penalty for a lesser crime, like driving while impaired. If that's the case, however, Phelps would not be eligible to received a probation before judgment this time and would have to admit to guilt and receive a conviction.

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