TEN years to the day since their mother was killed, Prince William and Prince Harry will today mark the poignant anniversary with a memorial service watched by a worldwide television audience of millions.

The brothers were only boys when Diana, Princess of Wales, was killed in a car crash in Paris, and they bravely walked behind her coffin at her funeral.

Now grown men of 25 and 22, they will step up in front of the 500-strong congregation at the Guards' Chapel in London after planning every detail of the service, helped by Diana's family.

The Duchess of Cornwall will stay away from the service after criticism that it was inappropriate for her to attend.

She will head to her countryside retreat Ray Mill in Lacock, Wiltshire - the private family home she still owns and kept on after her marriage to the Prince of Wales.

She pulled out of the live televised commemoration at the weekend, explaining the u-turn by saying she did not want to detract from the purpose of the day.

William and Harry invited their stepmother, but the decision caused controversy.

Her presence was always going to be problematic, with some adamant it was not right for the woman who had an affair with Charles while he was still married to the Princess to be there.

The Queen, the Duke of Edinburgh, Charles - now without his wife at his side - and more than 30 royals will gather along with Diana's siblings Earl Spencer, Lady Sarah McCorquodale and Lady Jane Fellowes.

Sir Elton John, Sir Cliff Richard, Lord Attenborough and celebrity photographer Mario Testino - all friends of the late Princess - were invited by the princes.

Prime Minister Gordon Brown and former premiers Tony Blair and Sir John Major will also be among the guests.

Both William and Harry will give readings at the service, as will Lady Sarah McCorquodale. But there will be no address from the Princess's brother, Earl Spencer.

Charles Spencer's controversial ''blood family'' eulogy at the Princess's funeral in 1997 was seen as an attack on the royals.

Diana's favourite hymn will form the emotional finale. I Vow To Thee, My Country was sung at both her wedding and funeral.

The hour-long service, which begins at noon, will be conducted by the Reverend Patrick Irwin, Chaplain to the Household Division.

Floral arrangements, organised by the Spencer family, will include rosemary for remembrance and English garden roses, which will be given to some of Diana's favourite charities afterwards.

Among family, friends and those the Princess met through her charity work will be 12 of her godchildren, her godparents and all of the bridesmaids and pageboys from her 1981 wedding to the Prince of Wales.