The widower of charity fund raiser Jane Tomlinson said that failure was "not an option" as he set off today on a gruelling journey to mark the tenth anniversary of the first time his wife completed the London marathon.
Mike Tomlinson, 51, will run the Paris and London marathons with his daughter, Rebecca, 24, and both will complete six days of cycle rides between the two events to cover a total of 650 miles.
Mrs Tomlinson, who died in September 2007 aged 43, inspired thousands of people with her charity challenges while battling terminal cancer, including the London marathon, Florida Ironman competition, and a 2,500 mile bike ride across America.
She raised more than £1.85 million in seven years, despite her pain and illness, and her family has continued to raise funds for her charity, the Jane Tomlinson Appeal, since her death.
While collecting his marathon race pack in Paris yesterday, Mr Tomlinson said: "It's the thought of Jane. Failure is not an option for us. We can't not do it. However painful it gets we just have to keep going.
"I'm very nervous, it wasn't until I looked at the route that I realised I'm running 43 kilometres, (26.8 miles) then cycling 60 kilometres (37.5 miles) on Monday.
"It's daunting, I'm not going to lie. Before Christmas I was training at a half marathon distance but I got injured. For the last four weeks I've done nothing. I'm not fit but I am fresh."
After tackling the French run today, they will cycle to Zeebrugge in Belgium. From there they will get the ferry to Hull and travel through the Tomlinsons' home turf of Yorkshire, before arriving in London ahead of the marathon next Sunday.
It is estimated Mr Tomlinson will need to consume 4,535 calories a day for the race, including an average 750g per day of carbohydrates.
Rebecca Tomlinson, 24, Jane's daughter and an events co-ordinator for a charity, said she was spurred on by the memory of her mother and the support of the Appeal, and "knowing that there's a group with me and that it's the tenth anniversary of mum doing the London marathon".
She added: "I'm looking forward to it but I'll be glad when it's finished. I'm a bit worried about how much pain I'll be in because I was too scared to take any medical advice, but I have done a marathon before."