Queen will headline Sonisphere festival.

The legendary 'We Will Rock You' group have signed up former American Idol singer Adam Lambert to step into the shoes of late frontman Freddie Mercury, who died in 1991, for The Rock festival, which tours across Europe in July.

Adam told the Daily Star newspaper: "The intention is to pay tribute to Freddie and the band by singing some f*****g great songs. It's to keep the music alive for the fans and give it an energy that Freddie would have been proud of."

Adam first met original Queen members Brian May and Roger Taylor when he performed with them on the final of American Idol in 2009, and they last appeared together last November at the MTV European Music Awards in Belfast, Ireland.

The Sonisphere tour will include a date at Knebworth in the UK, the venue where the band played their final show with Freddie before his death.

Adam denied he was trying to take the place of the iconic singer, adding: "After the EMAs, I heard faint little slithers of a backlash from people saying: 'You can't replace Freddie Mercury.' But I already knew that.

"There's no intention in my mind of replacing Freddie. That's impossible."

Since Freddie's death, Queen have released one posthumous album, 'Made in Heaven' in 1995. In 1997 bass player John Deacon retired and has not been replaced with a permanent member.

Brian and Roger continued to tour under the Queen name, with Free singer Paul Rodgers, between 2004 and 2009.

Although Adam is now singing with the group live, Brian has said any future releases will be built around unreleased tapes of Freddie singing.

He said: "There is a couple of very interesting tapes with Freddie singing with Michael Jackson that we're looking at.

"Those kind of things we can work on together and it's nice that in a sense Freddie is still involved in it."

Other acts rumoured to play Sonisphere - which takes in France, Poland, Switzerland, Turkey Greece and Italy, among others - include Faith No More and Green Day.