PRINCE William revealed tonight that he proposed to Kate Middleton using the engagement ring of his mother, Diana, Princess of Wales.

The Prince is to marry Kate Middleton next year, Clarence House said today.

William and his long-term girlfriend, Kate Middleton, got engaged on holiday in Kenya last month and will marry next year.

Miss Middleton, showing off the distinctive blue sapphire engagement ring alongside her husband-to-be tonight, told reporters that joining the Royal Family was a daunting prospect.

But she added: "Hopefully I'll take it in my stride."

Prince William said of their engagement: "The timing is right now, we are both very, very happy."

Explaining why he decided to give Diana's ring to Miss Middleton, William said: "It was my way of making sure my mother didn't miss out on today and the excitement, and the fact that were going to spend the rest of our lives together."

Asked about the proposal, Miss Middleton said: "It was very romantic, and it was very personal."

Asked if he got down on one knee to propose, William replied: "That's going to stay a secret."

Breaking the news earlier in the day, a statement from Clarence house said: "The Prince of Wales is delighted to announce the engagement of Prince William to Miss Catherine Middleton.

"The wedding will take place in the Spring or Summer of 2011, in London. Further details about the wedding day will be announced in due course.

"Prince William and Miss Middleton became engaged in October during a private holiday in Kenya.

"Prince William has informed The Queen and other close members of his family. Prince William has also sought the permission of Miss Middleton's father.

"Following the marriage, the couple will live in north Wales, where Prince William will continue to serve with the Royal Air Force."

The Queen is "absolutely delighted" at the news of the engagement, Buckingham Palace said today.

A Buckingham Palace spokeswoman said: "Both the Queen and the Duke of Edinburgh are absolutely delighted for them both."

Miss Middleton can trace her family back to County Durham. Her great-great-great-great grandfather, James Harrison, began work at Hetton Lyons pit, Hetton-le-Hole, when it opened in 1821.

Throughout the 19th Century, James and his son and grandson toiled in appalling conditions underground.