Rio 2016 silver medallist Siobhan-Marie O'Connor has announced her retirement from swimming after flare ups in her ulcerative colitis ruled her out of Tokyo 2020.
O'Connor, 25, missed Team GB's Olympic swimming trials in April after suffering from another flare up in her colitis.
Ulcerative colitis is a chronic, life-long condition that affects the lining of the large intestine that causes weight loss, extreme fatigue and a weakened immune system.
"It was a really emotional time when I had that flare up [earlier this year]," O'Connor told ESPN. "I felt like my body was letting me down, which was really sad. But at the same time, I sort of want my retirement to be positive. And although I'm not going to Tokyo, I'm massively proud of everything I've achieved in my career.
"It's quite nice to think that everything I sort of set my mind on or wanted to achieve, I did achieve. And although I've had my health struggles, and it's sad that I've come to the end a bit sooner than I would have liked -- I did want to be in Tokyo -- I feel very grateful for everything I've achieved, and I have no regrets. I had a career I'm so proud of."
O'Connor was first diagnosed with the condition after London 2012 at the age of 16, which were her first Games.
The swimmer went on to win silver at Rio 2016 in the 200 metre individual medley with a new British record in the event, as well as being a part of the GB team to break the 4x100 medley world record at the FINA World Championships in 2015.
O'Connor also became a two-time Commonwealth champion and double European champion during her nine-year career.
"Stepping away from the sport that I love has been the hardest decision I have ever had to make," O'Connor added in a statement. "I am very disappointed that I haven't been able to compete at the Tokyo Olympics this summer, but I am proud of all that I achieved in my career.
"I have been blessed with so many amazing opportunities during my time as an athlete that I will forever be grateful for. I have travelled the world, worked with incredible and inspiring people and made friends for life.
"I fell in love with the sport when I was eight years old. Back then, I never could have imagined all of the places that it would take me and the memories that I would make."