Williams said: "If this doesn't get me a knighthood, nothing will. I can't wait for the show."
"The Diamond Jubilee concert will celebrate the 60 years of the Queen's reign with an amazing lineup of world-class artists coming together to play at one of the biggest and most exciting live music shows in recent years," Barlow said when the event was announced in February.
"With Buckingham Palace as a backdrop, it's going to be a fantastic event which transcends multiple decades of music. It'll be a great, unique, experience for the thousands attending, watching on TV and listening on radio. I can't wait."
Kylie Minogue, Steve Wonder, The Voice coaches Sir Tom Jones and Jessie J, Ed Sheeran, Sir Elton John, Sir Paul McCartney, Dame Shirley Bassey and Annie Lennox are among the artists who have already been confirmed for the Queen's Diamond Jubilee concert.
The show takes place at the Queen Victoria memorial in front of the Palace, and will be broadcast live on BBC One and BBC Radio 2 in the UK.
Highlights will be made available on June 5 on ABC for viewers in the United States.