In his new book, “Endgame: Inside the Royal Family and the Monarchy’s Fight for Survival,” royal researcher Omid Scobie claims Taylor Swift declined an invitation to sing at King Charles’ coronation celebration in May.

Scobie did not explain why the “London Boy” singer declined the assignment, but she was performing her last of three Nashville gigs on the king’s day.

The Post contacted Swift’s rep for comment.

The historical event apparently called for several musicians. Harry Styles, Adele, Robbie Williams, and the Spice Girls had better things to do.

The “Rocket Man” superstar declined to perform due to schedule issues, according to his rep.

“The royal family has faced a number of p.r. disasters in recent times, and anyone performing at the show would have to consider whether there would be a backlash from appearing among their fans,” publicist Simon Jones told Rolling Stone in March.

The scarcity of accepted invites contrasted with Queen Elizabeth’s Platinum Jubilee. One year ago, Alicia Keys, Diana Ross, John, Andrew Lloyd Webber, Duran Duran, Nile Rodgers, Lin-Manuel Miranda, Rod Stewart, and Andrea Bocelli performed.

“American Idol” judges Katy Perry, Lionel Richie, Andrea Bocelli, and Take That performed at Charles’ Windsor Castle royal event for 20,000 people.

However, Richie admirers were “disappointed” by his voice and performance, comparing it to Kermit the Frog or a karaoke bar novice.

Princess Charlotte, daughter of Prince William and Kate Middleton, sang along to Perry’s “Roar” and “Firework.”