A young couple cancelled their engagement party at the last minute to take part in a night-time fundraising walk for a cancer charity - and were joined by all 62 of their guests.
Harry Vickers and Emma Thornton Jones, from Clapham, south London, put their plans on hold because Mr Vickers' father Tony is very ill in hospital with cancer.
Instead of celebrating their good news with a party in their favourite pub tonight, they and their guests joined more than 16,000 people to walk through London to raise money for Cancer Research UK through its Shine Night Walk.
They only decided on their change of plan at the start of the week, leaving their guests with no time to prepare for their half marathon walk.
Mr Vickers, 27, said: "Very sadly, the doctors told us dad isn't going to be around for the wedding so we decided to focus on the engagement party. But last week, dad had a serious health wobble and we just felt a party didn't feel right.
"I had seen posters advertising Shine, which raises money for Cancer Research UK, and it just seemed that doing something like that would be the right thing to do - part celebration but also doing something that recognises the battle dad has fought for the last two years and supporting research that can save lives.
"So at the 11th hour, we announced we were going to do Shine instead and asked the guests if they would like to join us. The response was phenomenal. At least 30 people came straight back and said they had friends or family affected by cancer and wanted to sign up straight away.
"One rushed straight out and bought 100 glow sticks. The response far surpassed our expectations."
The couple set off on the 13.1 mile walk - which takes them from Southwark Park to Old Billingsgate in the heart of London - at 7.30pm with a champagne toast to Mr Vickers, 71, who is following their progress from his hospital bed.
The group, which includes Harry's mother Pippa, involves walkers aged between 19 and 70. Others taking part can complete a full marathon.
Mr Vickers, who works in renewable energy, said: "Dad is the most ridiculous party animal and would have loved the pub night. As it is, he is in hospital so this seemed like a much more appropriate way of celebrating our two families coming together.
"There is of course a very sad element to this. But everyone is affected by cancer and doing this seemed the most positive response to the situation. To have our family and friends with us, literally every step of the way, felt great."
His father, a former managing director of BSkyB, was diagnosed with bowel cancer two years ago. In tribute to his avid support for Norwich City, Mr Vickers and his fiancee, 31, named their fundraising team Tony's Tigers and wore yellow and green ribbons.
The couple, who are due to get married next June, have already doubled their original fundraising target and have raised around £8,000.
Gemma Jones, spokeswoman for Shine, said: "Harry, Ems and all their guests taking part in Shine is an amazing gesture. We are pleased and honoured to have shared their special night. It was always going to be a night to remember but this has made it extra special.
"They and all our 'Shiners' have helped make a real difference to people's lives."
Money raised through Shine funds research into all 200 types of cancer or 12 specific types of cancer including lung, bowel, breast, prostate, children's cancers, brain, skin, ovarian, leukaemia, pancreatic, cervical, and testicular.
To sponsor the couple, visit www.justgiving.com/TonysTigers.