From The Sun in the UK:

"MADONNA and JUSTIN are the surprise headline guests signed up for Radio 1’s Big Weekend in May.

Justin told Radio 1 bosses earlier in the week that if Madge was up for it, so was he.
No1 ... Madonna and Justin
She signed on the dotted line on Friday, so he will be game to get involved too.

Madonna has driven a hard bargain, though.
She won’t do any interviews and she’ll be in and out of the festival faster than a beer down CHRIS MOYLES' throat.

The full lineup for the Big Weekend will be announced today with Moyles kicking off the ticket rush on his breakfast show.
The mini-festival, in Maidstone on May 10 and 11, has become a big event in the music calendar.

Source: The Sun