The shock American play, which has been tipped for New York’s Broadway, shows Diana’s former lover Hewitt wearing just his boxer shorts as he caresses Diana next to bed.
Feet away Prince Charles embraces Camilla Parker Bowles by a neighbouring bed as the actors play out the “crowded” marriage and Charles and Diana.
The musical, called “Diana”, depicts the pair’s adulterous goings-on with their lovers as their marriage famously broke down and ended in divorce and, later, Diana’s tragic death.
One scene recreates how the princess wore a strapless dress to a party on the night Charles admitted he had cheated on her with Camilla.
Encouraging her to attend an event, a male character believed to be based on butler Paul Burrell tells Diana: “You are going and you’re going to wear a ‘f*** you’ dress.”
Another shocking scene shows the paparazzi swarming around Diana at the start of her and Charles’ relationship while they sing a song called “Snap, Click”, reports Mail Online.
“I don’t think Prince William and Prince Harry would be very happy with this”
Other songs include Welcome To The Windsors, Here Comes James Hewitt – about Diana’s ex-Army captain lover – and Secrets and Lies.
The eyebrow-raising musical was only this week preview at the La Jolla Playhouse in San Diego, California, before the official opening night on March 3.
Its run has been extended to April 14 and tickets are reportedly selling fast.
But critics and audience members have slammed the production as tasteless and disrespectful to Diana’s sons, Prince Harry and Prince William.
Ingrid Seward, editor in chief of Majesty magazine, told the Mail: “It is in such bad taste that it’s best ignored.”
And asked if members of the Royal Family would watch it, she added: “Oh goodness no, none of them would have any interest in it.”
One audience member who saw the show also said: “I don’t think Prince William and Prince Harry would be very happy with this.”
The script is by Joe DiPietro and the score by David Bryan, who was the keyboard player in rock band Bon Jovi.
The pair have previously won a Tony Award for best musical for Memphis – based on one of the first white DJs to play black music in the 1950s.
Meanwhile Diana is played by English actress Jeanna de Waal, 30, who studied at the Liverpool Institute of Performing Arts.