Visitors of the Museum of Fine Arts were treated to an impromptu performance of "O Holy Night" by Berklee students and Boston musicians on Saturday, December 14.

In the video released Wednesday, musicians slowly gather around a cellist in MFA's Shapiro Family Courtyard, followed by a choir and solo vocalist Mark Joseph.

Joseph said he was surprisingly at ease as he stood up to sing.

"I just told myself, 'Mark, don't stress. Yeah you've got one chance but whatever, sing the song and do your best to get the message across. And keep it simple,'" he said.

You'll get chills as you watch and listen to the video below.

Students Evan Chapman and Josh Knowles came up with the idea a few months ago. The pair were brainstorming ways to share music outside of Berklee's community, said Chapman, who graduates Thursday.

"Three weeks before the flash mob I was visiting the MFA and was taken aback by the room and was inspired by the space and felt it would be a perfect location to share one of my arrangements," he said.

The choir rehearsed twice together and then the whole group, including strings and singer Mark Joseph, a 20-year-old Berklee student, practiced together on Friday.

Chapman arranged the music and flash mob around specific instrument sections so they could begin at different times to build up the feeling of uncertainty and surprise.

"A few onlookers could sense that something may be happening as we were trying to sneakily set a few things up right beforehand but the response during and after the performance was really wonderful as people who came to visit the museum got up from their tables to watch," said Chapman.

"The mood as I sang was very calm," said Joseph, who was trying to not over sing or add too many riffs. "Like almost an out-of-body experience. It was really cool."

In total, there were over fifty performers singing the holiday song and four audio engineers and seven videographers to capture the act.

This was the first public performance from the group at Berklee, Loft Sessions.

"Judging by the response we've received in reaction to this video and performance I can definitely say there will be more in the future," said Chapman.