Watch: Rihanna & Eminem preview their 'Monster' tour at Lollapalooza...

Lollapalooza kicked off last night, which saw Rihanna and Eminem preview their upcoming 'Monster' tour. The superstars performed their #1 collaborations 'Love The Way You Lie' and 'The Monster.' Plus, Rihanna took over Dido's verses for Em's hit song 'Stan.' Watch a preview of their tour inside, which kicks off next week.

Rihanna brought a little goth to her look, rocking next season's Givenchy! It would have been nice to see them perform 'Numb' but they can't offer up all the tour spoilers in one night could they?

Thoughts?