The Rocket Man singer will be singing at the Magic Summer Live festival at Hatfield House later this year in July along with Rumer and the Lighthouse Family.
John will be performing on stage with The Overtones, who are currently enjoying chart success with their album Good Ol'Fashioned Love.
One of its members used to be a waiter at some of the singer's parties.
Lachie Chapman told UK newspaper London Evening Standard: 'I used to serve Elton John's table when I worked in a restaurant, which he booked out for his Xmas party two years in a row!
'He was always really lovely and now we are sharing a stage with him. It's mind-blowing.'