Billy Monger says he was close to breaking point after battling jellyfish stings and crosswinds en route to smashing the Ironman record for a double amputee at the World Championship.
The 25-year-old former racing driver completed the 226.3km (140.6 mile) course at Kona, Hawaii in 14 hours 23 minutes 56 seconds on Sunday, more than two hours inside the previous record.
Monger completed the 3.8km swim in 1:07:29, the 180km cycle in 7:26:50 and the marathon run in 5:26:26 and said he "wouldn't have dreamed in a million years" he could beat the record by such a margin.
"The mental strength required to do an event of such duration I think that, at times, was close to breaking me," Monger told BBC Radio 5 Live.
"In the swim I got stung by a jellyfish in the first 100 metres. That set the tone for the pain that was going to come my way.
"Then towards the end of the swim I got stung by an even bigger jellyfish. I was lucky because some people who get stung it can rule you out the race entirely."
Monger's legs were amputated after he was involved in a near-fatal crash while racing at Donington Park in 2017.
He has since moved into broadcasting, featuring in the BBC series Celebrity Race Across the World and completing Billy's Big Challenge in 2021, when he walked, cycled and kayaked across Britain and raised more than £3m for Comic Relief.
As well as the jellyfish stings Monger pinpointed a point at 90km of the cycle as one of the "moments where it was a real struggle".
"There was a really hard climb and that, with huge crosswinds coming into play and me being a double amputee and having my right leg generate most of my power, means that balance is affected," he explained.
"That was a bit of a struggle and I had to grind my way up the long steep hill."
One of Monger's legs is amputated above the knee and the other below. His prosthetics were adapted to make running more comfortable.
When Surrey-born Monger started training he struggled to run 5km without feeling pain from his prosthetics, but the biggest change he made was to his running style.
"We've had to reinvent through this whole journey, and whole process, how I run," he explained.
"When I first started running on prosthetic legs I would run in a conventional way, rather than circumduction which you might see from the way Paralympic runners run.
"Eventually I went to that style of running and that changed the game for us."
Monger acknowledged that representing TeamGB at the 2028 Paralympics in Los Angeles in the Paratriathlon is potentially on his radar in future.
"Funnily enough, having spent a year of my life training for triathlon and the Kona Ironman, my trainers Mark and Will, they've been slowly drip feeding me a little bit of a hint here and there about LA in 2028," he added.
"It's definitely something they've been just easing me into the thought process of, that that Paralympic Games is four years away but it could be a possibility.
"I've loved the process of training for Kona and I've learnt a lot through this whole experience so I would definitely never say never."