US President Barack Obama is proving to be a swimming fan.
Less than a day after sending out a rare personal tweet to congratulate the most decorated Olympic athlete ever, Obama called Michael Phelps on the pool deck to hail his performance.
Phelps, still reeling from the previous day's tweet, described the call as "pretty cool".
"I answered the phone and the voice said 'Michael?' 'Yes.' 'Please hold for the President of the United States," he told reporters, after qualifying for the 100 metres butterfly semi-final.
"I was like, 'wow'."
The president, he said, told Phelps the country was supporting him and proud of his performance.
"He finished by saying 'make sure you tell your mum I said hi'."
Phelps' mother Debbie, who raised Phelps and his two sisters single-handedly, is considered to be a great contributor to his success, helping him with his hyperactivity, and egging him on from the stands at every meet.