Neil Harper, of Hemel Hempstead, has already completed the London Marathon, and a two-mile swim, with only the 100-mile London to Surrey bike ride to take on to complete the London Classics Challenge.
Neil’s determination to fundraise began when he met eight-year-old James Dodd, who has a form Mitchondrial (Mito) disease.
The 39-year-old mechanical engineer said of his 100-mile bike challenge: “It is going to be a tough ride but no matter how hard it gets I know the pain is temporary, unlike James and others like him who battle Mito every day.
“That is what keeps me going in those dark moments when you are starting to doubt yourself.”
Neil has been raising funds for the Lily Foundation, a charity for families affected by Mito since 2016.
Since being involved with the charity he has tackled 30 events including a 100k London-Brighton Marathon and the Three Peaks Challenge.
He added: “They provide a brilliant service for children like James and their families, and fund scientific research to find treatments for a cure.”