Nurse Samantha Varney is competing in today's marathon for Get Kids Going, which helps disabled people up to the age of 26 take part in sport.
The 22-year-old, of Somerton, near Bicester, is aiming to raise £1,500.
She said: “I am really excited. The nerves have worn off. I went to collect my race number in London and seeing everyone there made it real.
“I feel quite proud to be running the marathon. It is a dream come true.
“I know it is going to be hard, but I will be focused mentally. I will have so many people in my mind as well as the charity I am running for. I will do whatever it takes to get across the finish line.”
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