London Marathon runners splashed royals, smashed records and saw each other across the line as thousands pounded the streets of the capital.
The Duke and Duchess of Cambridge and Prince Harry were on the sidelines to cheer the heroics of 39,487 racers, the most to ever complete the 26.2-mile course.
But when William and Kate dished out water to parched competitors they were forced to dodge showers of liquid from the crowd powering past them.
As runners crossed the finishing line in the afternoon sunshine, an act of comradeship between two men became one of the day's defining moments.
Swansea athlete Matthew Rees sacrificed his own race time to shoulder the weight of stricken David Wyeth, carrying his rival the final yards to the end.
Speaking to the Press Association, the 29-year-old said: "I saw him try to stand up again and his legs just went down again, and I thought 'this is more important, getting him across the line is more important than shaving a few seconds off my time'."
He added: "This is what the marathon is about - it's about people - it's for everyone. Moments like this make it worth it. I'm just glad he's okay."
Images of the pair instantly drew comparisons to champion triathlete Alistair Brownlee who supported brother Jonny to the end of a race last year.
Organisers said the final athletes completed the course at 6.15pm, leaving 561 who did not finish.
This year wacky records were conquered by the dozen, ranging from the fastest runner in Wellington boots to the quickest carrying a tumble drier.
Guinness World Records said the day saw a total of 39 successful efforts.
Among the famous faces who completed the feat for good causes were radio personality Chris Evans and Olympic rowing gold medallists Heather Stanning and Helen Glover.
Former Top Gear host Evans, running for his third consecutive year to raise cash for Children in Need, said he had struggled to contend with the sunshine.
"It was definitely the toughest it had ever been," he said.
"I don't know why that was, I think it might be because it was hotter, maybe I didn't train as hard, but it was really much harder than it had ever been before."
EastEnders star Adam Woodyatt had a more emotional journey as he watched his son, who just months ago was left unable to walk when he was run over, complete the race.
The Ian Beale actor, who finished in seven hours, said: "He was in a wheelchair for eight weeks, had to learn to walk again which he did really quickly, then he had to run which he did really, really quickly, then he went back to doing his gymnastics and all his tumbling really, really quickly.
"It has been pretty miraculous and then he goes and runs this in four hours and 24 minutes."
Earlier, British wheelchair champion David Weir stormed to his seventh victory in the race as speculation rumbles over his retirement.
A world record was smashed by Kenyan Mary Keitany, who claimed her third London Marathon crown by beating Paula Radcliffe's women's-only world best.
Daniel Wanjiru then made it double glory for the African nation when the Kenyan athlete claimed first place in the men's elite race .
Hundreds of police, including armed officers, were on duty to keep about 800,000 spectators and runners safe, barely a month after crowds were targeted in the Westminster terror attack.
Among the racers battling the tarmac were a couple beginning an unconventional honeymoon, having tied the knot aboard the Cutty Sark on race day.
Jackie Scully, who has just completed treatment for breast cancer, wedded partner Duncan Sloan on the historic ship just hours before they both crossed the start line.
As the election race heats up, it was the Conservatives who got their noses in front in the athletics, when Rehman Chishti beat 15 other competing MPs with a time of three hours and 34 minutes.
Ken Jones, the oldest runner at 83, completed the course in six hours and 41 minutes - rounding off his 37th consecutive London Marathon.
William, Kate and Harry sent the runners off by pressing a large red button, after their campaign, Heads Together, was selected as the London Marathon's official charity.