Royal watchers are hoping that Prince Harry will make a surprise appearance on stage for his grandmother the Queen during a star-studded concert in her honour.
Take That star Gary Barlow, who has helped to organise the event, did not quash the rumour when asked if the royal would play the tambourine for the crowds, saying "we'll see".
Harry played the instrument on the Diamond Jubilee track Sing, written by Barlow and Andrew Lloyd Webber, which will be played on Monday night.
The Queen is expected to attend the event despite Duke of Edinburgh being taken to King Edward VII Hospital in London as a precautionary measure with a bladder infection.
Take That star Gary Barlow, who has helped organise much of the concert, reacted to the news of Philip's illness by saying: "It's sad, really sad."
A host of music legends will perform for the Queen on a stage erected in the shadow of Buckingham Palace. Stevie Wonder is among the all-star list of artists performing, as are Sir Paul McCartney, JLS, Sir Elton John and Kylie Minogue.
Other acts are Will.i.am. Sir Tom Jones, Jessie J, Dame Shirley Bassey, Annie Lennox and Ed Sheeran.
Barlow said: "This has been 18 months in the planning tonight so it feels like it's all come to a head at last. What we've tried to do this evening is try to represent all the years of her reign. So music across 60 years, artists that span 60 years. So the repertoire tonight will cover all of those decades."
Asked about Harry playing on stage he said "We'll see," then added: "There's a few surprises tonight, I think you've all been staring up on the roof there, there is an act on the roof, there are a few surprises to come so we'll see."
There are 18,000 people invited to the show - 10,000 ballot winners and 8,000 people from charities associated with the Royal Family. Spectators will be able to watch the concert from the Mall and large crowds have already built up in the thoroughfare, with some sleeping overnight to be sure of a good spot.