Less than two years after he retired as the most decorated Olympian ever, Michael Phelps is diving back into competition next week — a move that could lead the Baltimore swimmer to his fifth Summer Games in 2016.

Phelps will compete in the Arena Grand Prix, held in Mesa, Ariz., from April 24 to 26, USA Swimming announced Monday. It is his first competition since the London 2012 Games that brought his total medal count to 22, 18 of them gold.

"The One has returned," swimming analyst Mel Stewart said, in what was typical of the delighted response to Phelps' decision. "He is Mr. Swimming."

At 28, Phelps has already accumulated an unprecedented haul of medals, world records and accolades. He took more than a year off from training after London but eventually returned to the familiar lanes at North Baltimore Aquatic Club, first to get back into shape and eventually to test the competitive waters.

Monday's announcement confirmed what many had long suspected — that Phelps was not quite ready to retire from the sport he ushered into greater prominence than ever before. In November, U.S. Anti-Doping Agency records revealed that the swimmer had re-entered the drug testing pool mandatory for competition, the clearest sign yet that he had not shut the door on a possible return to racing.

But while the 2016 Games in Rio de Janeiro loom, Team Phelps is taking a more measured approach of seeing how he does in one competition before committing to others.

"We have discussed a long-term plan in general terms, but until he swims in a meet, we're not going to know," his longtime coach Bob Bowman said Monday. "Will he be eighth? Second? Sixteenth?

"I think he certainly won't be embarrassed swimming in the meet," Bowman said, "and I think he will be competitive. The difference is, he is doing half the training he used to."

Phelps has been training with a host of Olympic stars who increasingly have been drawn to NBAC in Mount Washington, including Yannick Agnel of France, Lotte Friis of Denmark and Americans Allison Schmitt and Conor Dwyer.

While the teenage Phelps famously didn't take a single day off from training during one five-year stretch, at this point in his career, he is focusing on shorter and fewer races.

His agent, Drew Johnson, said Phelps plans to enter the 50- and 100-meter freestyle and the 100-meter butterfly races in Mesa. Previously, he was better-known for longer distances, such as his signature 200-meter fly and the grueling 400-meter individual medley that includes all four swim strokes.

Still, Phelps on any starting block is cause for excitement: Ticket sales doubled at the Skyline Aquatic Center in Mesa, and requests for media credentials also increased compared to previous meets in the current Grand Prix series, said John Martin, sports communications manager for USA Swimming.

Frank Busch, director of the U.S. National Team, said he was thrilled that Phelps had returned to competition, however long it lasts and whether the Mesa meet leads to further events.

"We're getting someone back in our sport who is the most decorated athlete in Olympic history," Busch said. "We couldn't be happier. Michael continues to raise the bar for our sport."

Busch said he expects Phelps to take it one meet at a time before deciding if he'll try for Rio. "If he feels like it's not clicking, maybe he'll step back," Busch said.

Olympic swimmer and NBC commentator Rowdy Gaines said he was "overjoyed" by Phelps' return.

"He's our Babe Ruth, our Michael Jordan," Gaines said.

Perhaps more than most, Gaines understands the pull of the pool — he too retired after missing out on the 1980 Games boycotted by the U.S., but returned to win three gold medals in 1984.

"When I retired in 1981, I meant it. But I realized it was something I loved and I came back," he said. "Michael misses the limelight. He misses making an impact. Swimming is in his DNA, so why not come back?"

Both he and Stewart, who runs the Swim Swam website, said they were not surprised by Phelps' decision, especially after seeing him at last year's world championships.