Story highlights Olympic swimmer Michael Phelps apologizes to people he "let down"

22-time Olympic medalist is arrested on a DUI charge

A Land Rover he was driving in Baltimore was stopped for speeding

Phelps, 29, returned to swimming in April, about two years ahead of next Olympics

Legendary Olympic swimmer Michael Phelps, the most decorated Olympian of all time, was arrested early Tuesday in Maryland on a DUI charge, according to the Maryland Transportation Authority.

Phelps, known as the "Baltimore Bullet" and winner of 18 Olympic gold medals, was arrested at about 1:40 a.m. and charged with driving under the influence, excessive speed and crossing double lane lines within the Fort McHenry Tunnel on I-95 in Baltimore, the authority said in a statement. He was later released.

Phelps, who returned to competitive swimming in April, said on his official Twitter account that he understands the severity of his actions.

"I know these words may not mean much right now but I am deeply sorry to everyone I have let down," Phelps, 29, said in a series of three tweets.

USA Swimming issued a written statement Tuesday afternoon.

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

A Maryland Transportation Authority police officer was operating a stationary radar on southbound I-395 leaving Baltimore when a white 2014 Land Rover passed traveling at 84 mph in a 45-mph zone.

The officer followed the vehicle onto northbound I-95, through the tunnel and stopped the Land Rover just beyond the tunnel's toll plaza.

The 22-time Olympic medalist was identified as the driver by his driver's license and appeared to be under the influence, the statement said.

"He was unable to perform satisfactorily a series of standard field sobriety tests," the statement added. "Mr. Phelps was cooperative throughout the process."

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Previous run-ins with the law

It was not Phelps' first DUI case.

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In 2004, he was arrested on charges of driving under the influence in Salisbury, Maryland. He pleaded guilty and was sentenced to 18 months probation. He also issued an apology after that incident.

In 2009, a photograph surfaced of Phelps allegedly smoking pot from a bong at a party.

"I'll make a million mistakes in my life but as long as I never make the same mistake again, then I've been able to learn and grow," Phelps told CNN in 2012. He also said that the incident made him realize who his real friends were.

After the bong incident, Phelps was suspended from competitive swimming for three months and one of his sponsors said it would not renew his contract

USA Swimming, the nation's governing body for competitive swimming, said it was withdrawing financial support for Phelps and barring him from competition during the period of his "reprimand."

Kellogg Co. said it would not renew his advertising contract.

"Michael's most recent behavior is not consistent with the image of Kellogg," company spokeswoman Susanne Norwitz said at the time.

At the time, Phelps admitted "regrettable behavior" after a British newspaper published the photograph. The tabloid News of the World showed Phelps using the bong during what it said was a November party at the University of South Carolina in Columbia.

Back in the water

In April, back in the pool for the first time since 2012 , Phelps was close to his peerless best and raced to a second-place finish in the 100-meter butterfly final in front of a sold-out crowd at the Skyline Aquatic Center in Arizona.

Phelps retired after the 2012 Olympics and embarked on a year of travel and golfing, with little mention of a return to swimming.

But he sparked speculation about a potential comeback by re-entering the U.S. Anti-Doping Agency's testing program last November -- which began a nine-month wait required before a swimmer can again compete.

When the question of a return to Olympic action arose -- with a potential fifth games in Brazil in 2016 -- Phelps would only say he is taking "one step at a time."

In August, he won five medals at his first international meet -- the Pan Pacific Championships -- since the Olympics. Phelps won the 100-meter butterfly and was on Team USA's winning 800-meter and 400-meter medley relay teams. He took silver in the 200 individual medley and 400-meter freestyle relay. He was selected as the United States Olympic Committee's male athlete of the month.