Originally the site of a Saxon manor built in 857 AD, Leeds Castle stood first as a earthen compound surmounted by a wooden palisade with two wooden towers. Mention of this castle reaches as far back as the Doomsday Book of 1086, King Edward the Confessor gave it over to the House of Godwin, and eventually the stone castle settled into the hands of the Norman Crevecoeur family. In 1278, King Edward the 1st took ownership, making extensive amendments to its design. Later noteworthy occupants included Henry VIII. The last resident was Lady Baillie who updated the castle with 20th century amenities in the 1920s.
It isn't clear through the record exactly whose dog this might have been--but then, it may never have had an owner. If an omen, this spectral black dog might exist as some sort of entity outside our understanding, one that only assumes this familiar shape.
Other paranormal phenomena have been reported here as well.
While visiting the castle, Alice Pollock, a sensitive, was touching objects in hopes of a psychometric experience. She instead experienced something of a slip in time as the room she was in slowly shifted to a more ancient iteration. There she spied a tall woman in a white dress walking through the room. This experience only lasted a brief moment before Alice found herself pulled back into present day.