"I literally had to put my hand over my mouth at times because it was such a big secret... It was really hard. I even went on an American tour and didn't tell anyone. I heard the reports that it was going to be Sir Elton John or Jay Z performing at their reception while all the while it was me." Ellie Goulding's performance at the wedding of Prince William and Catherine, Duchess of Cambridge last year (11) was a hard secret to keep.