Adam Lambert is joining Queen as its lead singer -- the rumors were true. But it turns out it could be only a short-term arrangement. Queen announced on its website this week that the former American Idol singer will join them for their headlining set at Sonicsphere in Knebworth, UK, in July.

The website announcement specifically says it's a "one-off concert." Still, you never know.

“Judging by my incoming mail, this decision will make a lot of people very happy," Brian May said. "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.”

Knebworth Park is a monumental location in the history of Queen. It was Aug. 9, 1986 when the band last played there on what was to be the last show of their Magic tour, which completed a comeback that began with Live Aid. It was also the last time Freddie Mercury performed in public with Queen.

"I remember Knebworth as being the most incredible gig, with the most amazing audience and the sound on stage was utterly perfect," Roger Taylor said. "It was a fitting last stand before a live audience for Freddie. It will be a real challenge to complete the circle by returning with Adam."

Lambert isn't short on words either.

"I'm completely in awe of the Queen phenomenon," Lambert said in the announcement. "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. I know the evening will be a huge milestone for me, and with the support of Brian, Roger and the rest of the band I know magic will be on display.”