Sierra Swan joined Smashing Pumpkins frontman Billy Corgan in a performance of ‘Willingly’ on Monday (August 31) at Hotel Cafe during the final stop of the Billy’s tour with Spirits In The Sky. The song is originally by Willie Nelson and Shirley Collie. “I had so much fun and Billy’s new songs are amazing,” Swan wrote on her MySpace. “Everyone in the band sounded great! Linda Strawberry looked beautiful and sang beautifully as well. Thank you Billy for including me in such a beautiful show.” Watch it via YouTube below.