Claire Squires, the runner who collapsed and died during the London Marathon, was competing to raise money for the Samaritans in memory of her brother, who died from a drugs overdose, friends and family have said.
Her brother Grant Squires, who suffered from depression after a car accident in which his girlfriend died, is reported to have died after taking an overdose drugs in 2001.
Claire's brother was just 25 when he ended his life.
A friend of the family told the Daily Mail: "To lose one child is just terrible, but to lose another – it’s a nightmare. They are a lovely family, and all the siblings were really close, so it was awful for them when Grant died. Now to lose Claire as well, it is just awful."
Donations have been pouring in for the 30-year-old's chosen charity since her death. By Tuesday morning the account had raised almost £300,000 for charity.
Squires' mother, a care home manager, volunteered for the Samaritans for 24 years, according to The Telegraph.
"I'm running the london marathon for Samaritans because they continuously support others" Squires Just Giving page declared.
"It was just going to be for fun. but its a fab opportunity to raise money for my charity the Samaritans if everyone i know could donate £5.00 that would be a great help and change lives." she wrote.
Squires, from North Kilworth in Leicestershire, fell to the ground as she made her way along Birdcage Walk, near St James' Park, on the final stretch of 26.2 mile course.
Tests to establish her cause of death are expected to take place in the coming days. She is the 10th person to die taking part in the London Marathon since it started in 1981.
Close friend Nicola Short paid tribute to Squires describing her as an "inspiration" who brought laughter and love to everyone's life.
The pair climbed Mount Kilimanjaro for the RAF Association last year, raising £1,500 for the charity.
Paying tribute on the association's website, Short said: "Claire is an inspiration to us all. She brought laughter and love to everyone's life. She will be sorely missed by all.
"Our thoughts and prayers are with her family and friends at this time."
In a statement on its website, the association, which works to support serving and former RAF personnel and their families, said: "It is with great sadness that the RAF Association has heard of the tragic death of Claire Squires, 30, following the London Marathon on Sunday.
"Claire was a wonderfully vibrant and energetic person, who was a keen charity supporter and loved by all who knew her. Claire's efforts in support of the RAF Association helped to raise hundreds of pounds for our charity and that is something for which we will always be grateful.
"In 2010 she climbed Mount Kilimanjaro and also took part in other fundraising events in support of the RAF Family in recent years."
Catherine Johnstone, chief executive of Samaritans, said the organisation was deeply saddened at news of her death.
She said: "We are devastated following the tragic death of one of our marathon runners and are supporting the family through this very difficult time. Our thoughts are with everyone who knew her.
"We appreciate all that our marathon runners do; it is with their support, commitment and fundraising efforts that that we are able to offer our vital service for people with nowhere else to turn." the 26.2 mile course. She was given medical attention by paramedics but died at the scene.