Violinist Joshua Bell was a sweaty, disgusting mess when we spotted him following a performance at Union Station in Washington, DC ... but he was a sweaty, disgusting mess with a $15 million violin in his hands!!!
After working up a lather doing a charity gig ... Bell explained the violin -- a 301-year-old Stradivarius called the Gibson ex Huberman -- was now worth 8 figures after he bought it for about $4 mil. Understandably, Bell says he takes the instrument with him everywhere.
Fun fact: Tuesday marked Bell's first show in a D.C. Metro station since his infamous video in 2007 ... where he played anonymously in a subway station for 45 minutes and pocketed a measly $32.17 from passersby and only got recognized once.