According to auctioneers Henry Aldridge and Son, from Wiltshire, the instrument is made of maple and spruce wood and belonged to Wallace Hartley, the leader of the orchestra on the ill-fated ship.
They have spent six years researching the object and even enlisted world leading forensic scientist in Oxford and used a CT scanner in Swindon to prove it was authentic.
But as the violin is about to go on public view at the visitor attraction, Titanic Belfast, the relative of another band member says he simply "does not believe" it is genuine.
Christopher Ward lost his grandfather, Jock Hume, in the tragedy. He was 21 years-old and himself played the violin. Mr Ward has spent years researching the subject for a book, And the Band Played On.
He told ITV News the way violins were made a century ago meant is was unlikely it could have survived for several days in the water after the Titanic went down. "It would have broken up" he believes.
But the auctioneers disagree. They say they "wanted proof beyond doubt" it was genuine before they sold it. They have spent six years and many thousands of pounds on world forensic experts and historians to discover if it is the real thing.
They say the inscriptions on the violin itself and the case that was with it prove beyond doubt it is genuine.
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