Kris Cook was taking part in the 100-mile ride through London and Surrey on the Olympic road race course when he suffered a cardiac arrest.
The tragedy struck at Newland Corner in Guildford, 46 miles into the route. He was treated at the scene and taken to hospital, but he was later pronounced dead.
"Kris was part of a group of 12 riders raising money for Woking Hospice. His mother said that he had died doing something he loved and welcomed donations in Kris's memory to his Woking Hospice fundraising page," said a spokesman for RideLondon.
"The organisers of the Prudential RideLondon-Surrey 100 would like to express their sincere condolences to Kris's family and friends."
Kris was riding the course - which had been shortened to 86 miles due to severe rain - with his girlfriend, Nicola Tait. He had told her that he would "meet you at the top of the hill", but collapsed minutes later.
"There were no paramedics at the top of Newlands Corner, just a couple of support vehicles," Nicola told Get Surrey.
"He was given mouth to mouth while we waited 20 or 30 minutes for the ambulance to come.
"The paramedics gave him electric shock treatment and then he was taken to hospital.
"I had to go home and wait. The police called and came round to see me and I also spoke to a Prudential organiser who had a medical background and said the situation was looking grey."
Hundreds of well-wishers have visited Kris's fundraising page on the internet to leave their condolences, and over £20,000 has been pledged to his chosen charity following the tragic turn of events.
Nicola called on more people to follow suit and help his sacrifice mean something.
"People have got to sponsor him, I really want him to raise as much money as he possibly can," she added.
"It is going to help the family and the whole situation. I really want everyone to know, he was just the most wonderful person, he was so beautiful, he looked after me and everyone.
"He was so kind and so generous, I just can't believe he was taken because it is just so unfair."
Kris's mother Sue told Get Surrey, "He was very caring and always cared about everyone else but himself. He didn't have a bad bone in his body and would always go the extra mile.
"I had worried all week that something would happen, maybe like a premonition that he would have an accident on his bike but I never thought this.
"We are of course shocked and Nicola is devastated, they had found each other, she had found her perfect partner and [they] were moving in together in September."
- Family & Relationships