A loving brother dedicated his 24th birthday to running the marathon in aid of a charity that is helping fight a rare disease afflicting his sister.
LAM Action supports women who suffer from the rare disease Lymphangioleiomyomatosis, which affects the lungs.
Nat Field, from Wimbledon, took on the 26.2 mile challenge on Sunday in aid of his sister Aimee, 28, who had the condition diagnosed in 2011.
Mr Field, who was running his first marathon, said: "One of the hardest things is the fact there was very little information on LAM because it is so rare.
"Aimee puts twice as much effort into everything she does as anyone else I know and she does it on 30 per cent of the lung function the rest of us enjoy, but she carries on with such good grace. "
He was able to complete the course in 3 hours and 45 minutes, and has so far raised £1,836.
To support him visit www.justgiving.com/Nathanael-Field1