Pop star Britney Spears is to appear before thousands of rock fans at a European festival next summer.
Spears' latest album has sold more than a million copies in the US
She will play at Portugal's Rock in Rio-Lisbon show on 5 June, alongside acts such as Slipknot, Metallica and Guns N' Roses.
Spears is on tour in the US in March and April, promoting her album In the Zone, which has sold 1.38 million copies in the country in five weeks.
Other acts at the Lisbon festival will include Sting and Alejandro Sanza.
The show is modelled on the original Rock in Rio festival which began in 1985 in Rio de Janeiro, Brazil.
About 70 acts will perform 120 hours of music during the two stages of the event on 29-30 May and 3-6 June. About 100,000 people are expected to turn up each day to see the performances at Lisbon's Bela Vista Parque.
Spears played at Rock in Rio in 2001 alongside acts such as REM, Sheryl Crow and Beck.