King Charles' Coronation Day Struggles To Find Celebrity Performers: Reports

King Charles III's coronation concert may not feature some of the U.K.'s biggest entertainers, according to reports.

Several British media outlets, including The Sun and the Daily Mail, reported that the palace is struggling to book famous names as performers for the highly anticipated Windsor Castle event on May 7, the day after the King is crowned. International Business Times could not independently verify the information.

The Daily Mail reported that Ed Sheeran and Adele are both unable to perform at the concert.

An unnamed source close to the 32-year-old "Shape of You" singer claimed to the outlet that Sheeran hasn't been invited but that the organizers of the event were told that he is "busy" and is set to perform at a show at the AT&T Stadium in Arlington, Texas, a day before the coronation concert.

Adele, 34, who is known for her chart-topping hits "Someone Like You" and "Hello," doesn't have anything scheduled for May 7 so far. It is unclear why she has opted to reject the offer to perform at King Charles' coronation concert.

The Sun reported that The Spice Girls, Harry Styles and Sir Elton John are also unable to perform or attend the concert, citing conflicting schedules.

"Organizers are working against the clock to pull together an exciting line-up but have hit a series of challenges," an unnamed source told the outlet. "Elton John was top of Charles' list, but due to his European tour, which sees him performing in Germany the Friday before, [and] then again soon after the Windsor concert, he isn't able to make the dash to the U.K. work."

The source continued, "Man-of-the-moment Harry Styles is also tied up with touring and unable to get key band members together as they'll be on much-needed downtime."

Take That's Gary Barlow, Mark Owen and Howard Donald reportedly will be headlining the upcoming concert without Robbie Williams. Sisters Kylie and Dannii Minogue, Andrew Lloyd Webber and Lionel Richie have also been confirmed to perform, according to the Daily Mail and The Sun.

Olly Murs was reportedly also invited to perform, but organizers are still waiting for an official confirmation.

King Charles' coronation concert will be streamed live on BBC on May 7. Thousands of lucky royal enthusiasts may also get the chance to watch the concert in person as tickets will be made available to the public via ballot, Daily Mail reported.

An unnamed source told the outlet that more performers are going to be revealed in the coming weeks as the "biggest names and acts" in the music industry are being "approached" and "considered" for the show.

King Charles and Queen Consort Camilla will be crowned on May 6. The ceremony will be held at Westminster Abbey in London.