Willie Nelson had an extra band member on stage Tuesday night (June 17) in Boston, Mass. -- Oscar-nominated actor Johnny Depp.

Nelson was backed by his well-known Family Band, which included his son, Lukas. Depp stayed on stage for the entire set, with very little given by way of introduction.

"He just said something like, 'And that's Johnny over there playin' the guitar,' " a concert attendee recalls (quote via People magazine).

Depp was in Boston to film his upcoming movie, 'Black Mass.' But this wasn't the movie star's first encounter with Nelson. Earlier this year, he jammed with the 81-year-old during the annual music festival, SXSW, in Nelson's home state of Texas.

The actor's love of music extends far beyond the country music hitmaker. He has played on several projects over the years, including Oasis' 1997 record, 'Be Here Now,' and on the soundtrack for the movie, 'Once Upon a Time in Mexico.'

Tuesday was a big day for Nelson. In addition to sharing the stage with Depp, it was also the release of his latest studio album, 'Band of Brothers.' Purchase the project here.

Nelson's appearance in Massachusetts was part of his ongoing tour with Alison Krauss, which heads to New Hampshire and New York this weekend. A list of all of their upcoming shows is available here.