The seat of the Dukes of Northumberland is Alnwick Castle, in Alnwick, Northumberland; their London residence is Syon House in Brentford which replaced as their London residence the demolished Northumberland House in the Strand.
The seat of the Dukes of Northumberland is Alnwick Castle. This is in Alnwick, Northumberland. Their London residence is Syon House in Brentford. This Syon House in Brentford replaced as their London residence the demolished Northumberland House in the Strand.