Welsh singer Katherine Jenkins said she was running the London Marathon in memory of her father and to show solidarity to people affected by the bombings in Boston.
She said: "Like everyone else, it was just so devastating to see that on the news. But I think we all feel more than ever that we want to do this and show our support for Boston."
The 32-year-old, who has raised over £22,000 for a cancer care charity, added: "I wanted to run it in support of Macmillan. My father passed away from cancer when I was 15 and the Macmillan nurses came and they were wonderful."
She said: "I really don't think of myself as an athletic person at all. I never in a million years thought I would do this. I'm glad that I am, but I am nervous."
ITV News' Royal Correspondent reflects on running the London Marathon in the shadow of one of Africa's most endangered species.
Tens of thousands of runners turned out for the London Marathon in a show of solidarity to the Boston bomb attack victims.
London Marathon runners will wear black ribbons and observe a 30-second silence to honour the victims of the Boston Marathon bombings.