It has been reported that Britney Spears has called on ex Justin Timberlake to join her on her 2009 ‘Circus’ tour. The singer – who has recently made her comeback – has recieved a mixed reception from fans and the media, and it is said that Spears is relying on others to help make the tour a success. Other acts that have apparently been roped in are Madonna, Elton John and Pharrell Williams.