Adele and Harry Styles are believed to have turned down the opportunity to perform at the Platinum Jubilee weekend.
The Platinum Party at the Palace was one of the main highlights of the four-day celebrations to honour the Queen's 70 years of service earlier this month, where a host of global superstars took to the stage outside Buckingham Palace for the two-and-a-half hour concert on June 4.
Organisers of the concert were keen to include Los Angeles-based Adele, 34, following her impressive return to the spotlight last year.
Their hopes were dashed though after Adele, who was awarded an MBE for services to music in 2013, snubbed the approach.
A source told the Daily Mail: "They were told she couldn’t do it. Scheduling issues, or something like that, were given as an excuse.
"It caused a lot of surprise, particularly as she was awarded an MBE. After all, how many chances will there be to perform in front of Buckingham Palace for the Queen?"
Former One Direction star Harry, 28, is in the midst of a world tour but that did not clash with the Platinum Party at the Palace and he headlined Radio 1's Big Weekend in Coventry the week prior.
No explanation was given for Harry's rejection to the invitation, with a source simply saying: "He was asked".
Her Majesty the Queen had a comedy cameo to start proceedings to the concert as she enjoyed a cup of tea and a marmalade sandwich, which she had in her handbag in case of "emergencies", with Paddington Bear.
The pair then started tapping teaspoons on their teacups to the rhythm of Queen's hit song We Will Rock You as the British rock band and Adam Lambert opened the star-studded event, with singing sensation Diana Ross closing the show in her first live performance in the UK for 15 years.
Other acts such as Alicia Keys, Duran Duran, Andrea Bocelli, Nile Rodgers, Diversity and Eurovision star Sam Ryder also performed on the evening.
Tributes were made to the Queen by the likes of Sir David Attenborough, David Beckham, Dame Julie Andrews and Emma Raducanu throughout the concert, which was attended by many members of the royal family including the Duke and Duchess of Cambridge, their children George and Charlotte, the Prince of Wales and the Duchess of Cornwall.
Her Majesty the Queen could not attend the show due to experiencing "some discomfort" during the first day of the celebrations.
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