Oh, woe! I rather feared as much. Thank you, both, for the information.
However, 'scion' need not necessarily mean 'son of'. It occurs to me that he could have been the son of the Duke's married daughter, with a name other than Percy.
I am grateful to Fiddler for this information about Viotti (not Viotto), and the information confirming that Hills did handle the sale of a Stradivarius that he had owned:
http://entertainment.timesonline.co.uk/ ... 392674.ece
It's clear that Marrocco's narrative is not wholly true; but I am curious enough to pursue this a little further. It would be intriguing to know how the story came about, if it is a fiction; or to discover any links, however tenuous, with the truth.
I think I really will have to contact the archivist at Alnwick Castle to see if he can offer some elucidation or dismiss the whole thing as a fiction. The Duke of Devonshire's archivist at Chatsworth was extremely helpful and enthusiastic about the poems written by the Duke and Duchess that I was given permission to publish in my little anthology so maybe I will receive similar help from Alnwick.
Watch this space.