Rocket Man teams with Purple One for London encore

Prince fans attending his latest concert in London Thursday night got a taste of two musical legends when, after the main concert, Elton John joined the U.S. pop icon onstage.

John appeared unannounced onstage at the start of the encore and sang the Beatles song The Long and Winding Road accompanied by Prince on guitar.

"You know who it is," Prince told the crowd after their performance. "Sir Elton John!"

Prince then proceeded to launch into seven more songs for a lengthy encore set, including his own hit When Doves Cry and the Gnarls Barkleynumber Crazy.

The Minneapolis-born singer then played an intimate after-show for a further two hours, which included such songs as the Beatles' Come Together and Led Zeppelin's Whole Lotta Love.

Earlier in the evening, the audience had cheered when the video monitors at London's O2 arena showed John enjoying the show.

Prince is close to wrapping up a 21-date concert series at the London arena, with his final gig scheduled for Sept. 21.

An anti-piracy firm representing the musician revealed on Thursday that Prince is in the process of launching lawsuits in Britain and theUnited Statesagainst websites posting unauthorized audio and video clips of him. At the same time, he is targeting companies selling unauthorized Prince merchandise online.