When Jules is fixing Milo's tie for the ball, she comments "Oh 007, eat your heart out." Roger Moore (Duke Edward) played James Bond in seven movies.
The Castlebury castle is actually Peles Castle, the Royal Palace of the Romanian Kings, which can be found in Sinaia, Romania. It is unique in Europe in terms of architecture, internal decorations, and collections.
Sam Heughan (Ashton, Prince of Castlebury) actually has royalty lineage in his bloodline, this was confirmed in a 2014 interview.
Lady Kristina, whom Duke Edward (Roger Moore) greets as he enters the ballroom, is Roger Moore's real-life wife Christina 'Kiki' Tholstrup.