Gary Barlow and Cheryl Cole are rumoured to be performing a duet at the Queen's Diamond Jubilee Concert on Monday.
The Mirror reports The Girls Aloud star, who is not on the official line-up, will make a surprise appearance and perform live in front of the global audience.
The duo are expected to sing Need You Now in front of the 10,000 Diamond Ticket winners, and a TV audience expected to reach tens of millions.
Barlow will also perform his special Jubilee single, Sing, which he created with Andrew Lloyd Webber. It features performers from across the UK and the Commonwealth, the Military Wives Choir and even has Prince Harry playing a tambourine.
Also taking to the spectacular stage built around the Queen Victoria Memorial, right in front of Buckingham Palace, for the show in honour of the longest reigning monarch since Queen Victoria, are music veterans Tom Jones, Paul McCartney, Stevie Wonder, Cliff Richard, Elton John and Shirley Bassey.
Gary's Take That bandmate Robbie Williams, English tenor Alfie Boe, Aussie pop princess Kylie Minogue, Grace Jones, The Overtones, Renee Flemming, Lang Lang, Annie Lennox and Jools Holland will also perform.
Along with relative newcomers to the charts Jessie J, Ed Sheeran, JLS, Will.i.am and Gareth Malone and The Military Wives.
Meanwhile, The Daily Mail have reported 80s group Madness will play a rendition of their top ten hit Our House from the roof of the palace and may alter the lyrics of the song to honour their royal host.
Hosting the event, which every senior member of the Royal Family is expected to attend including Prince Charles and the Duchess of Cornwall, the Duke and Duchess of Cambridge and Prince Harry, will be comedian Lenny Henry, Lee Mack, Peter Kay and Miranda Hart.
Lee Mack has spoken of his terror about presenting at the Concert, he told The Sun: "It's not usual to do gigs in front of the Royal Family... there's always that voice in the back of your head saying, 'Don't swear, don't swear,' and that makes you want to swear."
The performance will conclude with the Queen lighting the National Beacon, the last in a network of over 4,000 lamps across the UK to celebrate the Jubilee.
Watch The Diamond Jubilee Concert on BBC1, 7.30-10.45pm