Applegate, who has Asperger’s Syndrome, was only 16 when she won the 200m freestyle S14 final in London – a triumph that led to her being appointed an MBE.

But she has suffered injury and health problems during her career and needed surgery in 2016 after experiencing breathing problems for more than a year that she put down to asthma or a chest infection.

She bounced back to win two silvers and a bronze at the Rio de Janeiro Games in the same year.

Following her 4x100m gold in Tokyo in 2021, the Paralympics having been postponed for a year, she suffered serious back problems, including a torn disc, a couple of years later.

Applegate decided against surgery and won her third world 200m gold in Manchester, regaining the freestyle S14 title she had first won a decade earlier.

But after competing in the trials for Paris with a sprained ankle, she did not make the Great Britain team to compete in the French capital.

In her Instagram statement, Applegate said:, external “Since my Paralympic debut in 2012, I’ve had the honour of representing Great Britain on the world stage and achieving 44 international medals.

“Swimming has been my life for as long as I can remember, and competing for my country has been one of my greatest privileges.”

She added: “This isn’t the ending I imagined, but it’s still a story I’m proud of.”