Madonna has recruited fellow pop star Britney Spears to appear in a video being made for her upcoming world tour.

The singer's spokeswoman has confirmed the film will be made into some sort of virtual appearance.

The 49-year-old's publicist, Liz Rosenberg, said: "There is footage being shot of Britney Spears some time this week - the rest is 'a secret'."

Madonna kicks off her Sticky & Sweet tour on 23 August in Cardiff before going to Wembley Stadium in September.

She then travels through Europe and North America before finishing in Miami on 26 November.

Madonna guest-starred in a music video for Spears' single Me Against the Music in 2003.

The pair stirred up controversy that year with an open-mouth kiss at the MTV Video Music Awards.