<P> Longford Castle is located on the banks of the River Avon south of Salisbury, Wiltshire, England . It is the seat of the Earl of Radnor, and an example of the Elizabethan prodigy house . </P> <P> In 1573 Thomas Gorges acquired the manor (at the time written "Langford"), which was originally owned by the Servington (or Cervington) family . Prior to this the existing mansion house had been damaged by fire . In c. 1576 Thomas Gorges married Helena Snakenborg, the Swedish born dowager Marchioness of Northampton and Lady - in - waiting to Queen Elizabeth . They rebuilt the Longford property as a triangular Swedish pattern castle on the banks of the River Avon . The building work became very expensive due to problems with the subsoil . Sir Thomas Gorges, who was now governor of Hurst Castle, persuaded his wife to beg of the Queen a shipwreck he knew from the defeated Spanish Armada . The gift was granted and the gold and silver retrieved from the shipwreck funded the completion of the castle under the final supervision of John Thorpe in 1591 . The family lived in the castle for several years before its final completion . </P>

Where is the castle used in princess diaries