Grammy-nominated violinist Philippe Quint expressed his great gratitude for a New Jersey cab driver who recently returned his beloved (and very expensive) Stradivari by performing a special concert for his benefactor.

Violinist Philippe Quint played a private concert for a cabbie and his fellow co-workers at Newark Liberty International Airport on Tuesday, as a thank you for being returned his 285-year-old Stradivari.

Quint left his precious instrument, a 1723 Antonio Stradivari “Ex-Kiesewetter,” in the cab of Mohamed Khalil on the morning of April 21, when he was returning from a performance in Dallas.

The violin’s value is estimated at $4 million and is on loan from philanthropists Clement and Karen Arrison, of Buffalo, N.Y., reports the Associated Press.

Quint contacted the Port Authority of New York and New Jersey, as well as the Newark Taxi Commission. Khalil had parked his car for the night and was not aware of the commotion. Upon learning of it the following day, he contacted Quint and returned the irreplaceable instrument.

Quint performed for an audience of about 200 cabbies Tuesday, including Khalil. He performed solo numbers as well as a blues number with guitarist Michael Bacon, brother of actor Kevin Bacon, reports the AP.

Khalil, 57, emigrated from Egypt in 1980 and became a U.S. citizen. He has been driving cabs for 24 years and is married with three sons. He was awarded a medal last month by Newark Mayor Cory A. Booker. He and his family will attend a performance by Quint at Carnegie Hall on Sept. 23.

“I usually have a conversation with a customer, I feel like they are my guest for however long the ride is,” Khalil told the AP. “He told me he was a musician and he was coming back from a concert. I didn't know he had a valuable violin with him. Lots of people have left things in my cab, but this is the most valuable thing anyone has left.”