Michael Phelps

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Michael Phelps competes in the 100-meter butterfly during the Arena Grand Prix swim meet, Thursday, April 24, 2014, in Mesa, Ariz. It is Phelps' first competitive event after a nearly two-year retirement. (AP Photo/Matt York)

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Michael Phelps talks with a fellow swimmer after practice, Wednesday, April 23, 2014, in Mesa, Ariz. Phelps is competing in the Arena Grand Prix at Mesa, as he returns to competitive swimming after a nearly two-year retirement. (AP Photo/Matt York)

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Michael Phelps swims during a training session Wednesday, April 23, 2014, in Mesa, Ariz., as he prepares to compete for the first time since retiring after the 2012 London Games. The 22-time Olympic medalist is entered in three events at the Arena Grand Prix starting Thursday. (AP Photo/Matt York)

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Michael Phelps, right, speaks to the media after practice as coach Bob Bowman listens Wednesday, April 23, 2014, in Mesa, Ariz. Phelps is competing in the Arena Grand Prix at Mesa on Thursday as he returns to competitive swimming after a nearly two-year retirement. (AP Photo/Matt York)

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Michael Phelps dives during practice, Wednesday, April 23, 2014, in Mesa, Ariz., as he prepares to compete for the first time since retiring after the 2012 London Games. The 22-time Olympic medalist is entered in three events at the Arena Grand Prix starting Thursday. (AP Photo/Matt York)

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Michael Phelps swims during a training session Wednesday, April 23, 2014, in Mesa, Ariz., as he prepares to compete for the first time since retiring after the 2012 London Games. The 22-time Olympic medalist is entered in three events at the Arena Grand Prix starting Thursday. (AP Photo/Matt York)

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Michael Phelps speaks to the media after practice, Wednesday, April 23, 2014, in Mesa, Ariz. Phelps is competing in the Arena Grand Prix at Mesa on Thursday as he returns to competitive swimming after a nearly two-year retirement. (AP Photo/Matt York)

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Michael Phelps laughs while talking with coaches during a training session Wednesday, April 23, 2014, in Mesa, Ariz., as he prepares to compete for the first time since retiring after the 2012 London Games. The 22-time Olympic medalist is entered in three events at the Arena Grand Prix starting Thursday. (AP Photo/Matt York)