The King looks set to endure a third day of controversy as the war of words between Buckingham Palace and Diana's brother continues.

In the latest extract from Earl Spencer’s book serialised in the Daily Mail, Diana’s brother claimed that the late Queen Elizabeth II considered restoring his sister’s Her Royal Highness title, which she lost when she divorced Charles.

It comes after a dispute blew up between the King and Earl Spencer, who claimed the then-prince told him, “rest assured, we’ll forget her soon enough”, days after Diana’s death in 1997.

Earl Spencer further claimed in his memoir of his sister that the King sounded “giddily elated… like a lottery winner” when he rang the earl following the princess’ death.

In other passages of the book, the earl described how his sister drove “more than once” to the cliffs at Beachy Head in East Sussex and was “contemplating ending it all”, adding that “her love for her sons stopped her from going further”.

The excerpt went on to claim Diana told her brother “my husband is in love with his valet” after telling him she was going to get divorced.

The palace has....