EXCLUSIVE: King Charles and Prince William 'Having Last Laugh' as Charles Spencer's Diana Book Price is Slashed

King Charles and Prince William are believed to be "having the last laugh" over Charles Spencer's explosive Princess Diana memoir after its price was slashed and Piers Morgan threatened legal action over an admitted error, sources have exclusively told RadarOnline.com.

Charles, 77, and William, 44, have largely continued with business as usual despite allegations in Spencer's book, Swan Song: Diana, My Sister.

The book went on sale for $19 at Waterstones in Britain – around half its $37 recommended retail price – while TGJones also offered a 50 percent introductory discount on the book.

Spencer, 62, subsequently apologized to Morgan, 61, for wrongly linking him to the publication of intrusive photographs of Diana.

A royal source claimed: "There is a feeling that the Palace doesn't need to get dragged into a prolonged public fight with Charles Spencer because events surrounding the book are now speaking for themselves.

"Piers challenging a clear factual error, Charles having to apologize, and the prospect of legal action have inevitably raised questions about the book's accuracy. From a PR perspective, people around the King and William feel the argument has effectively been won without them having to say very much at all – and they feel like they are having the last laugh about the whole affair, seeing that the price of his book has already been slashed so dramatically."

Spencer's memoir includes the disputed allegation that Charles told him "we'll forget her soon enough" following Diana's death at age 36 in Paris in 1997.

Buckingham Palace responded unusually forcefully, saying the King was "mindful that the pain of fraternal grief can cloud reason, affect judgment and colour memory in ways others do not recognise."

Spencer stands by his recollection and has accused the King of "gaslighting" him.

But he was forced to concede a separate mistake after suggesting Morgan was responsible for the publication in the Sunday Mirror of photographs of Diana exercising in a leotard in 1993.

Morgan was working at The Sun at the time and did not join the Daily Mirror until 1995.

Spencer apologized, but Morgan said he still intends to pursue legal action against him and the publisher, Penguin.

Another source said: "Piers' intervention couldn't have come at a worse time for Spencer. The Palace had already challenged his recollection involving the King, and suddenly there was an entirely separate claim where Spencer himself accepted he'd made an error.

"Charles and William's approach has essentially been to get on with their jobs. The feeling is that responding to every allegation would only give the book more oxygen."

Charles was in Peterhead, Aberdeenshire, meeting Sea Cadets, the RNLI and organizations involved in the region's energy sector as Spencer's memoir reached bookstores.

Unveiling a plaque, Charles said: "I'm sorry it's taken so long to turn up here. I'm delighted."

William similarly maintained his public schedule, visiting ActOne, an independent cinema in Acton, west London, in his role as BAFTA president.

When asked by a reporter how he felt about his uncle's memoir, William did not respond.

Spencer has meanwhile said Prince Harry, 42, is "completely fine" with the book, which he maintains was written as a personal tribute to his sister rather than an attack on the monarchy.

Diana became one of the world's most recognizable women after marrying then-Prince Charles in 1981. Her marriage deteriorated amid intense media scrutiny, and the couple divorced in 1996.

Diana became celebrated for charitable work, including campaigns involving HIV and Aids awareness and landmines.

On August 31, 1997, aged 36, she died from injuries suffered in a car crash in the Pont de l'Alma tunnel in Paris.

Her passing prompted an extraordinary worldwide outpouring of grief and intense scrutiny of the way she had been treated by Charles and the wider royal family.