Adam Lambert is joining rock band Queen for one concert this summer, at Sonisphere 2012. The former American Idol singer tweeted: \"As many suspected, I can finally confirm: I have been invited by Queen to sing one very special concert! Sonisphere at Knebworth July 7th!\" He added: \"The thought of sharing the stage for a full set is so beautifully surreal. I\'m honoured to be able to pay my respects to Freddie\'s memory. He\'s a personal hero of mine and I am deeply grateful for the chance to sing such powerful music for fans of this legendary band.\" Adam had previously tried to play down his comments that he planned to perform a tribute to the late Freddie Mercury, the band\'s lead singer. He told his Twitter followers: \"Sorry to be coy about the details the past few weeks, but I made a promise to keep it under wraps as best I could.\" Queen\'s Brian May and Roger Taylor confirmed that the American singer-songwriter will perform vocals for the band\'s headline set on the second day of the rock festival, 26 years after Queen\'s final concert with Freddie Mercury at Knebworth in August 1986. \"It\'s a worthy challenge for us, and I\'m sure Adam would meet with Freddie\'s approval! And what better place to revisit, and walk those emotional paths than Knebworth? It will be a rush,\" said Brian. Adam, 30, has sung with Queen before. In 2009 he performed We Are The Champions on the US reality show that made his name and then last November he sang an eight-minute set at the MTV Europe Awards to celebrate Queen\'s Global Icon Award. From: Belfast