The Rolling Stones announced that Taylor Swift will join them tonight (June 3) for the third of three shows in Chicago, Ill. Previous special guests for the dates at the United Center included Sheryl Crow on May 31 and bluesman Taj Mahal on May 28.

It's not clear what song Swift will sing. On May 31 Crow came out to sing 'All Down the Line.' Taj Mahal performed 'Six Days on the Road' with Mick Jagger and company on May 28. Carrie Underwood joined the band in Toronto on May 25, singing 'It's Only Rock 'n' Roll.'

The band spilled the secret at their Twitter page, giving no hint as to which song the pop-country superstar will choose. Swift hasn't mentioned the cameo yet on her Twitter page. (Our hunch - for no particular reason? 'Wild Horses.')

The Rolling Stones have just seven more North American dates remaining on the 50 and Counting Tour schedule. In June they'll return to Canada for shows in Toronto and Montreal before playing Boston twice, Philadelphia twice and Washington D.C. on June 29. The final dates on their official touring schedule are July 6 and 13 at Hyde Park in London.