Nathan Adrian has announced that he has testicular cancer.
The five-time Olympic gold medallist went for a routine check-up and a flu shot, but doctors quickly found it was much more serious.
"Something didn't seem quite right," posted the 30-year-old on his social media accounts on January 25, 2019.
"After a few tests and visits with a specialist, I unfortunately learned that I have Testicular Cancer."
Swim superstar Adrian has won five gold medals at three Olympic Games: Beijing 2008, London 2012, and Rio 2016.
"On the bright side, we caught it early, I have already started treatment and the prognosis is good. I will be back in the water in a few short weeks with my sights fully set on Tokyo!" - Nathan Adrian
Adrian rules the pool in Rio
Nathan Adrian's most recent Olympics at Rio 2016 were spectacular, as his four medal haul proves.
Nathan Adrian: My Rio Highlights
Nathan Adrian: My Rio HighlightsThe best moments from the 2016 Summer Olympic Games
Nathan Adrian's explosion onto the U.S. scene happened when he was just 19 at the 2008 Short Course World Championships.
Just by qualifying the teenager had made his mark, but when he went and won the 100m freestyle and two relays, the world of swimming realised it was watching the birth of a new star.
Just as comfortable swimming individually as in a team, he made the U.S. 2008 Olympic swim team the same year, winning his first relay gold medal in Beijing.
He's never looked back.
Eight Olympic medals including five golds later, Adrian has provided some of the most dramatic moments in swim history.
One of those came at London 2012 when Adrian ended a 24 year U.S. drought in the 100m freestyle.
Adrian ends USA 100m freestyle drought | London 2012 Replays
Adrian ends USA 100m freestyle drought | London 2012 ReplaysNathan Adrian wins the 100m Freestyle by the narrowest of margins, ending a 24-year gold-medal drought for the United States in the event.
The 30-year-old has qualified for every major tournament since bursting onto the scene in 2008, including three Olympic Games and long course World Championships in 2009, 2011, 2013, 2015 and 2017.
He's been crowned world champion 10 times, winning 16 medals at long and short course Worlds overall.
An astonishing career that Adrian is intent on continuing.
"I have already started treatment and the prognosis is good. I will be back in the water in a few short weeks with my sights fully set on Tokyo!" - Nathan Adrian
Used to winning top honours at the biggest sporting events on the planet, Adrian sees this cancer diagnosis as an opportunity to champion another cause.
The swimmer wants to use his story to break taboos surrounding testicular cancer and men's health in general:
"I hope to share my journey in an effort to help break the stigma of discussing men’s health issues." - Nathan Adrian
"I’ve realised that too often we tend to avoid these important topics," he continued, "ignore the potential warning signs, and put off getting the medical help that we may need."
Cancer may be the biggest challenge of his career, but Nathan Adrian is not one to avoid adversity.
"I am keeping a positive attitude as cases such as mine are curable."