Pop star Justin Timberlake will star alongside real-life girlfriend Cameron Diaz in "Shrek 3" as the voice of one of the animated characters.

The singer is lending his vocal talents to the role of the young King Arthur in the fantasy feature, which also sees Eddie Murphy and Mike Myers returning to play Donkey and lovable ogre Shrek respectively, reports the Internet Media Database.

Producer Aron Warner has quashed rumours that "Charlie's Angel's" actress Diaz - who plays Princess Fiona - persuaded him to cast Timberlake claiming the singer was just right for the part.

"Our desire was to get somebody who is visible and had their own persona to bring to the table. Justin fit the bill perfectly," he said.

In the third film, Shrek has to teach Timberlake's character - King Harold's rebellious teenage nephew who does not want to be king - how to act like royalty. It is scheduled for release in May 2007.