FILE - In this March 21, 2017, file photo, Michael Phelps and his wife, Nicole Johnson, smile during an NBA basketball game between the Los Angeles Lakers and the Los Angeles Clippers in Los Angeles. If Phelps returns to competitive swimming, the demands of training would surely cut heavily into his family time. That's why, if he tries to predict what the future might hold, it doesn't include a sixth Olympics at Tokyo in 2020. (AP Photo/Jae C. Hong, File)
Olympic champion Michael Phelps has announced his intention to retire after the London Olympics.