The Queen is reported to have refused even to acknowledge her existence.

Queen finally acknowledges Camilla

But the monarch's decision to now accept an invitation to an event which she knew Mrs Parker Bowles would be attending, is seen as a deliberate step forward in relations.

Royal watchers say King Constantine may have played a hand in encouraging the meeting and ending the bridge between Queen and heir which has been a worry to the whole Royal family.

He also knows the prince's distress about the longstanding situation.

Prince Charles was said to be extremely upset that his mother would not attend his 50th birthday at Highgrove two years ago because Mrs Parker Bowles was a guest.

He was forced to tread a delicate public relations path since his marriage to Diana ended in 1996.

But after Diana's death there has been a slow charm offensive to gradually introduce Mrs Parker Bowles to the suspicious British public.

They went public in January last year which was followed by holidays together and joint appearances at charity dinners and performances.

Change of heart

The BBC's Royal Correspondent Nicholas Witchell said the Queen's persistent reluctance to formally acknowledge her son's companion was because of the problems the relationship could create for the monarchy.

The Queen is the Supreme Governor of the Church of England which has strict laws on the remarriage of divorcees such as Mrs Parker Bowles.

She will also remember how instrumental divorcees have been in the break up of other royal marriages.

'Life is too short'

Constitutional expert Lord St John of Fawsley said the meeting was a healing of a long-running rift within royal circles but it did not mean that a marriage between the Prince and the Mrs Parker Bowles was likely.

He said: "I welcome the fact that it has happened - life is too short for quarrelling. There are so many problems which afflict families today that it a very good thing that this potential rift between Her Majesty and the Prince of Wales has been healed.

"It is a long step from that to concluding that a marriage will take place between Mrs Parker Bowles and the Prince - but that is really a matter for them."

The Prince does not need the consent of the Queen but if the Royal Assent was withheld he would have to give a year's notice to the Privy Council.

Lord St John added: "This is a clear indication that the Queen would not use the Royal Marriages Act in this way.

"The Queen is cool in her judgment and she would have assessed the whole issue. She has clearly concluded that the time has come for them to end what has been a point of contention."