Lady Diana and the Prince of Wales Prince Charles
Prince Charles had last minute doubts about marrying Lady Diana, a new book claimsGetty

Prince Charles had second thoughts about marrying Princess Diana on the eve of their wedding, a new biography on the Prince of Wales claims.

The Prince was so riven by doubt over his marriage to Lady Diana Spencer that he reportedly told an aide "I can't go through with it," the night before their July 1981 ceremony.

The couple had enjoyed only a five-month engagement before the wedding and the book Charles: Heart of a King claims both parties considered pulling the plug on their nuptials.

Diana believed Charles had feelings for Camilla Parker-Bowles, author Catherine Mayer writes, while the "desperate" Prince panicked and said he could not go through with the marriage.

He had, Mayer claims, underestimated Diana's personal problems and soon learnt she was a complicated woman.

The unauthorised biography had already caused a stir ahead of its publication on Thursday (5 February) after claiming Charles would be reluctant to rein in his opinions on issues close to his heart, including the environment and architecture, when he succeeds Elizabeth as monarch.

It also portrays competing factions within his inner sanctum with rivalry and backstabbing in his court, and suggests he refused to yield to calls to prepare for life as King of England.

Clarence House has stressed that Mayer's account is unauthorised, while royal biographer Philip Eade claimed it was full of hyperbole.