In PIX: Michael Phelps, the father...

Michael Phelps claimed 21st Olympic gold medal of his career on Tuesday.

But the most successful Olympian of all time shared the limelight with his three month old son Boomer.

Like any first-time dad, Phelps is pretty gobsmacked by his son.

Boomer Phelps stole a bit of his father's thunder as the little guy watched from his mother, Nicole Johnson's, arms during his dad's races.

Dressed in a patriotic red and white colours with his father's initials embroidered on it, the newborn is a hit on social media.

Even as Phelps raced to victory, people all over the world could not help but gush over his baby boy.

Most of the evening, Phelps junior snuggled in his mother’s arms with his grandmother cheering.

Debbie Phelps is delighted in her son's role as captain of the men's Olympic swim team.

She credited his fiancee and their baby for helping make Phelps's inner circle stable and positive.

Phelps had been notoriously antisocial around the village at previous Olympic Games – earphones in, plugged into a zone, no visitors allowed – that led him to a record 22 Olympic medals, 18 of them gold.

But with the birth of his son on May 5, it finally let him open up to the world around him.

Phelps also led the US team into the opening ceremony, the American flag bearer.

• The Rio Olympics, on Rediff.com