Magic was already in the air Friday as the Philadelphia Orchestra prepared to play its “Sorcerers, Spells, and Magic” Valentine’s Day set at the Kimmel Center.

But it was an unexpected pre-concert duet that stole the show, hitting all the right notes as second trumpet Tony Prisk got down on one knee to propose to first violin Julia Li.

Before the orchestra began to play, Prisk, in a routine announcement video, asked those in the audience to remain seated at the conclusion of the performance, and silence their cell phones.

“But right now, you might want to take them out and start recording,” he added, “because this isn’t something you see every day.”

Li set her strings aside and began to tear up as her beaming soon-to-be fiancé walked across the stage, asking her to marry him. As she said yes, the audience erupted into the kind of applause usually saved for the end of a symphony.

“I had a sneaking suspicion it was going to happen,” Li, 30, later said. “But I still cried.”

The two met around six years ago, when they joined the orchestra. Prisk, new in town from Houston, and Li, who had lived in the city for years while attending the Curtis Institute of Music, said they bonded quickly while touring with a “tight group of friends” in the orchestra.

They quickly developed chemistry, Li said, and moved to a home in South Philadelphia about a year ago.

“It just felt right,” Prisk, 45, said. “She’s beautiful, talented, and smart, and we laugh a lot together, our sense of humor lines up really well.”

In marriage, Li said she’s “looking forward to more of the same.”

As for wedding plans, Prisk said he will take his cue from Li.

“It’s all up to her now,” he said. “I did my part.”

Sans proposal, the orchestra will play its “Sorcerers, Spells, and Magic” program again Saturday at 8 p.m., featuring John Williams’ score from the Harry Potter movies, Paul Dukas’ “The Sorcerer’s Apprentice," and a performance of Maurice Ravel’s "L’enfant et les Sortilèges.” Tickets start at $42.