Mark Cavendish fell heavily in a dramatic conclusion to the first day of the Tour de France as the world's greatest bike race returned to the UK.
British fans were denied a fairytale finish to the first stage as Cavendish crashed in the final sprint to the line in Harrogate.
He was left prone on the ground clutching his shoulder after colliding with another rider in the final yards. The Isle of Man rider was able to pedal across the line, but was wincing and clearly in pain.
The Duke and Duchess of Cambridge and Prince Harry looked shocked on the finish line when the commentator described Cavendish's crash.
Although it was initially feared Cavendish's tour could be over, team doctors later confirmed the British star had not suffered any broken bones.
Mark Cavendish comes crashing down during the final stages of the first stage of the Tour de France in Harrogate
Medical examinations indicate that he injured the acromioclavicular (AC) joint between his right shoulder and collarbone. His team Omega Pharma-QuickStep said a decision about whether he will take part in the next stage tomorrow will be taken in the morning.
The Isle of Man rider tonight apologised to supporters keen to see a British rider over the finishing line first after the iconic race crossed the Channel for the first time since 2007.
"I'm gutted about the crash today," the 29-year-old said.
"It was my fault. I'll personally apologise to Simon Gerrans as soon as I get the chance. In reality, I tried to find a gap that wasn't really there.
"I wanted to win today, I felt really strong and in a great position to contest the sprint thanks to the unbelievable efforts of my team. Sorry to all the fans that came out to support - it was truly incredible."
After the announcement of Cavendish's crash, Kate put her hands to her mouth and leant over the barrier to try and get a glimpse of the accident site 200 metres further down the road.
The thousands of people watching with her at the finish also gasped in unison when they realised he had gone down.
Cavendish was cheered when he slowly crossed the finish line looking shocked and in pain.
The royal party clapped the riders as they crossed the line and looked down the course for the stricken sprinter.
Cavendish limped back a few minutes later, passing right in front of the royal enclosure. William, Kate and Harry again looked shocked as they could clearly see his torn shirt and injured left arm and shoulder just a metre in front of them. Only half an hour before the royal trio had been chatting to Cavendish's mother who was a guest in the royal area.
The stage was won by German Marcel Kittel, who received the yellow jersey from Kate.
Defending champion and British hopeful Chris Froome finished sixth.
Earlier, more than a million people lined the streets of Yorkshire amid jubilant scenes as the Tour de France came across the Channel for the first time since 2007.
The riders were given a royal send-off by the Duke and Duchess and Prince Harry as the world's best cyclists descended on Leeds for the Grand Depart of the 101st Tour de France.
Cavendish is attended to by team medical staff after his crash
Crowds of cycling fans flocked from all over the country to Yorkshire to get a glimpse of the 198 racers passing through the county's striking scenery.
Two spectators were hurt as the action unfolded.
Police said a teenage boy was in a stable condition after he was airlifted to hospital with leg injuries after what police described as "a team vehicle which formed part of Tour de France convoy" hit the youngster.
Meanwhile a woman was also flown to hospital with head injuries after falling through a roof while watching the race.
Cavendish crosses the line with the assistance of his team
The intense interest in the event put a strain on local transport links, with delays and large crowds at Leeds and York stations as thousands tried to make it to Harrogate for the finish of the 190.5km stage.
Organisers said "well over" a million people watched along the route, with initial estimates suggesting there were 230,000 spectators in the centre of Leeds and more than 10,000 watched the riders on the steep climb at Buttertubs Hill.
Sir Rodney Walker, chairman of co-ordinators TdFHUB2014 Ltd, said: "Today has been a massive success with well over one million people enjoying the sporting action along the route. Spectators have had a fantastic day they will never forget and Yorkshire has been showcased to a massive global audience.
"It has taken a huge amount of planning and teamwork, so thank you to all of our partners, and especially our stewards and the Tour Maker volunteers for all of their hard work.
"Today has set the tone for the next two days, and we look forward to seeing more huge crowds lining the route to watch the world's best cyclists in action."
Earlier the Duchess set the riders on their way.
Wearing a bottle green Erdem coat over a green Suzannah dress and carrying a grey clutch purse, Kate cut the ribbon to officially start the race.
She was joined by her husband and brother-in-law Prince Harry as the trio welcomed the cyclists for the Grand Depart of the 101st Tour.
The stage was won by German Marcel Kittel, who received the yellow jersey from Kate
Crowds of fans cheered loudly as the cyclists gathered outside the 18th century stately home Harewood House, where they took off their helmets as they were greeted with a rendition of the French and British national anthems, performed by the Band of the Corps of Royal Engineers.
The RAF's Red Arrows delighted crowds by performing a flyover that left a trail of red, white and blue vapour - the national colours of France and the UK.
The Duke and Duchess and Prince Harry watched from just next to the start line as the teams sped down the hill and out of the park, and William was heard to say: "The only better view would have been on the back of one of those motorbikes."
Tomorrow the riders will arrive in York for a stage taking in some of the most challenging climbs in Britain, ending in Sheffield.
Cavendish's mother, Adele Towns, had left the royal box by time her son crashed.
Prime Minister David Cameron reacts as Mark Cavendish crashes at the finish of the first stage of the Tour De France in Harrogate
After she met the Duke, Duchess and Prince she said they had told her Cavendish seemed relaxed when they spoke to him on the start line four hours before.
Mrs Towns said: "They were very relaxed. They wanted to know all about cycling.
"They said they had met Mark at Harewood House and he seemed very relaxed."
Mrs Towns, who was with Cavendish's stepfather, Chris, said: "They said they've started watching cycling now and they love it."
She said she was "speechless" after meeting the royals, saying "they are lovely, lovely, lovely people".
"I'm honoured," she said.
Mrs Towns said she had been rooting for her son but said: "So are all the mothers of the riders today."
David Cameron wrote on Twitter: "What a dramatic finish to stage 1 of the Tour, sadly it wasn't Mark Cavendish's day.
"Yorkshire has done the UK proud today though, and we look forward to more tomorrow."
The royal party met a series of sports stars as they waited at the finish for the riders to appear in the centre of Harrogate.
William was heard to say to one of the visitors that he thought his son George was still a little too young for a bike.
One of the guests was paralympian Sarah Storey who was with her one-year-old daughter Louisa.
The Duchess took a great interest in the youngster, who is about the same age as George, and she chatted to her gold medal winning mother at length.
Another paralympian, Dame Tanni Grey-Thompson, was a guest in the enclosure and William invited her to watch the dramatic closing stage with him and his wife.
As the riders entered the final kilometre, the three royals were clearly as caught up in the excitement as the thousands of people surrounding them - sitting in grandstands, standing behind barriers and hanging from every available window and vantage point in the blazing sun.
The fire service had to bring in a huge aerial platform near the finish line to rescue spectators who had climbed onto a roof and could not get down.
Long queues developed at Harrogate railway station tonight as the massive crowds who packed into the town tried to leave.
All road routes in the area were also heavily congested as tens of thousands of people went home.
The town will never have seen anything like this in its long history.
Every street was packed almost to the point that no-one could move, especially in the area around the town's famous Betty's tea rooms, where a huge crowd watched the race unfold on a giant screen.
There was a carnival atmosphere in the town centre, with its many bars, cafes and restaurants all packed to the point that people spilled out into the streets.
And, around the race route itself, crowds more than 20 deep crammed behind the barriers to cheer Cavendish into the long, final straight.