SHE was a minor socialite who became the semi-official escort for the Prince of Wales. She was also one of the few people who could defuse her lover's mood swings.

This is not a description of the relationship between Camilla Parker Bowles and Prince Charles.

It is, instead, that of Camilla's great-great-grandmother, Alice Keppel, who went on to become the long-time mistress of King Edward VII - the great-great-grandfather of Prince Charles.

Princes and kings throughout the generations have always had mistresses, and for the women who became royal lovers, the innocuous title of mistress brought with it great power and influence.

One of the most powerful mistresses of her time was Barbara Villiers, the lover of King Charles II.

After seducing the king, she ensured she remained a long-term lover, despite Charles' keen eye for fresh blood.

Although she was married to Roger Palmer, her fruitful affair with the King bore her six children - five of whom were acknowledged by Charles - and the titles Countess of Castlemaine and later Duchess of Cleveland.

The promise of sex could also be used to gain more than the title of royal mistress.

The vivacious Anne Bolyn used her considerable charms to beguile Henry VIII, but instead of agreeing to become his mistress as Henry expected, she refused to give herself to him until she became his wife and Queen.

Although her plotting paid off, she paid the ultimate price when she was beheaded for treason - on trumped up grounds of infidelity.

Apart from Camilla, the only mistress who went on to marry her royal lover was American divorcee Wallis Simpson.

Mrs Simpson had met Edward, Prince of Wales, at a house party given by his then mistress Lady Thelma Furness.

After he became king, the obsessed royal looked at ways of making the relationship with the woman he loved official.

But the Government and the Church could not contemplate a twice-divorced woman becoming his Queen, and he renounced the throne in 1936.

The couple became known as the Duke and Duchess of Windsor.

Unlike her great-great-grandmother, Camilla will finally be given an official place within the Royal Family when she marries on April 8.

After Edward VII died in 1910, Alice Keppel found that life without his patronage could be cruel.

She was not even allowed to sign the book of condolence.