The royal visit of King George V to Downton Abbey was based on his real-life visit to Wentworth Woodhouse, a mansion in Yorkshire which was used in this movie for the ballroom scenes at Harewood House.
The mansion that King George V and Queen Mary visit after Downton Abbey, where the ball is held at the end of this movie, is Harewood House. Although the name of the village is pronounced as it is spelled (Hare-wood), the House and the title Lord Harewood are perversely pronounced Harwood, as was correctly done throughout this movie.
According to the Director's Commentary, Charlie Watson (Albert the Hall Boy) originally featured as a reoccurring extra in series 5 & 6 of the television version of Downton Abbey (2010). The film version marks Charlie's first role with lines. Director Michael Engler said that "it felt in a funny way similar to the story; which is the Hall Boy who becomes the Footman - it's like the extra who becomes an actor".
The visitors, King George V and Queen Mary (previously Princess Mary of Teck), were the grandparents of Queen Elizabeth II.