LONDON (Reuters) - Britain's Prince William will marry his long-term girlfriend Kate Middleton next year after an on-off courtship that has lasted nearly a decade.
The elder son of heir-to-the-throne Prince Charles and the late Princess Diana proposed to Middleton with the large blue oval sapphire and diamond engagement ring his mother once wore as Charles's 19-year-old fiancee.
"It's very special to me," William told reporters on Tuesday. "It's my way of making sure my mother didn't miss out on today and the excitement and the fact we are going to spend the rest of our lives together."
The two 28-year-olds will marry in the spring or summer of 2011, 30 years after Charles and Diana's spectacular but ultimately ill-fated wedding.
"I didn't realize it was a race, otherwise I would have been a lot quicker, but also the timing is right now, we're both very happy, and I'm very glad that I have done it," William told reporters in London as the beaming couple posed arm-in-arm for the cameras of the world press.
Diana, who was said to be the world's most photographed woman during her lifetime, was divorced from Charles in 1996 and died a year later in a car crash after a high-speed chase through Paris with the paparazzi in hot pursuit.
Middleton will now have to get used to the huge media attention that her role will attract, but she looked calm as she appeared with William, blinking at the glittering flashbulbs of the massed ranks of photographers.
In an informal interview with an ITN reporter, she said Diana was an "inspiration" whom she wished she had met.
She told reporters that becoming a royal was daunting, but she hoped to "take it in her stride" with William's help.
William said: "It's about carving your own future, no one is trying to fill my mother's shoes. It's about making your own future, your own destiny, and Kate will do a very good job of that."
It was the first time the future princess, who described the proposal as "very romantic", had spoken so publicly.
Although the couple had discussed their future, Middleton described the shock when William proposed during a recent holiday in Kenya.
Asked if she expected the proposal, Middleton said: "I thought he might have maybe thought about it, but no. It was a total shock when it came, and very exciting."
William had carried the ring in his rucksack for about three weeks before summoning up the courage to pop the question.
"Everywhere I went I was keeping hold of it because I knew this thing, if it disappeared I would be in a lot of trouble and because I'd planned it, it went fine," he said.
William's grandparents, Queen Elizabeth and Prince Philip, and other members of the royal family said they were delighted.
"(I'm) obviously thrilled, thank you very much," Charles told reporters during a trip to southwest England, before joking: "They've been practising for long enough."
A statement from Charles's office, Clarence House, said William had sought the permission of Middleton's father.
"They make a lovely couple, they're great fun to be with, and we've had a lot of laughs together," said Michael Middleton, adding that he and his wife thought the prince was "wonderful".
William's brother Harry said the engagement meant he would get a sister "which I have always wanted".
Prime Minister David Cameron said a "great cheer" went up when a meeting of his cabinet was interrupted by the announcement.
William, currently a search-and-rescue helicopter pilot in the Royal Air Force, met Middleton when they shared a house at university in Scotland in 2001.
They split up in 2007 because, newspapers said, Middleton, who had been dubbed "waity Katie" by the tabloids, was getting fed up with waiting for William to propose, but they got back together soon afterwards.
The engagement has been long predicted and rumors of an imminent announcement have swirled around for months.
"She has shown herself to be a lovely, dependable, loyal, trustworthy girl and she will be wonderful for him and wonderful for the royal family," royal biographer Penny Junor told Reuters.
Royal writer Ian Lloyd said the world had been waiting for a royal with the captivating presence of William's mother Diana.
"What she's got and what obviously Diana had was this thing of star quality, something that you can't manufacture, you've either got it or you haven't," he told Sky TV. "She's certainly got that extra special thing that makes people different."
Britain faces austere times after recording its biggest peacetime budget deficit, and Clarence House said the couple would be mindful of the economic situation.
"It will cheer people up as we go into the dark months," said novelist Christopher Fowler, 57, outside St Paul's Cathedral in London.
Charles's wedding to Diana in 1981 was Britain's most lavish ceremony of recent times and became the focus of enormous interest around the world.
Some 600,000 people crammed the streets of London to watch the wedding procession to St Paul's Cathedral, and Cameron revealed that he had slept on The Mall, the grand road leading to Buckingham Palace, the night before the wedding.
Additional reporting by Tim Castle, Stefano Ambrogi, Avril Ormsby, Anna Yukhananov and Estelle Shirbon; Editing by Tim Pearce