Watch List notes:

COMMEMORATIVE MEDALS. BRITISH MEDALS. Hugh Percy, First Duke of Northumberland (1714-1786), Restoration of Alnwick Castle, Silver Medal, 1766, by John Kirk, bust of the Duke right, dated 1764, rev view of the castle, 43.5mm (BHM 107, R3). Good very fine and extremely rare.
There are two varieties of this medal, of which this is by far the rarer, as reflected by Brown's RRR rating.

Estimate: £200-250