Sam Spencer gets a surprising accompanist.

The 27 year-old busker was playing his keyboard and singing “Ophelia” by his favorite band, The Lumineers, outside 315 Washington Street, when someone from the crowd that had gathered steps forward and begins to play alongside him. When they finish, Jeremiah Fraites, who wrote the song and is the co-founder of the band, tells Spencer his rendition of the song is “awesome,” and invites him to attend the band’s concert three days later at the Xfinity Center in Mansfield.