AceShowbiz - Sienna Miller missed out on Sir Elton John's annual charity ball in Windsor, England on Thursday, June 24 after falling ill with glandular fever. The "Rocket Man" 's White Tie and Tiara Ball is a highlight of the celebrity social calendar in the U.K., with Elizabeth Hurley, Sharon Osbourne and Kelly Osbourne and David Walliams all heading to the singer's Windsor estate for the lavish affair.

But Miller was forced to skip the festivities after succumbing to the viral infection, which is also known as infectious mononucleosis (mono). She tells WENN, "I can't make it, I have glandular fever." The "Alfie" star cheered herself up with a hair appointment in London's posh Mayfair instead.

At the ball, Sir Elton was excited to auction off an Audi A1 car painted in pink by British artist Damien Hirst to raise money for the Elton John AIDS Foundation. He said, "This is one of the most exciting auction items we have ever had for White Tie."