Britannian Imperial Family

The Holy Empire of Britannia is ruled by the Imperial family, descended from Sir Ricardo von Britannia, designated heir and lover of Queen Elizabeth III, which holds the highest positions within its government and military. For example, Clovis is the Third Prince while Lelouch is the Eleventh Prince. The numbering of the Imperial princes and princesses is sorted by gender and birth order. For example, Euphemia is the third born daughter, making her Third Princess and Clovis is third born son, making him Third Prince. The princes and princesses use the same nobilty particle as their mother, though the usage does not mirror any real-world method. The female members are entitled to elect a personal guardian called a "Knight," who are given authority and placed directly under their command, with their own unit. Cornelia's Knight is Guilford who, along with her, commands a unit of Knightmare Frames. Suzaku Kururugi also served as personal Knight to both Euphemia and Lelouch, after he became the Emperor of Britannia, while with the latter he donned the title of Knight of Zero. It can be assumed that there are more members in the imperial family as there is a gap between the Third and Eleventh Princes. Though not explicitly stated, Nunnally was likely Fourth Princess during her father's reign, but with the gap between Third and Eleventh Princes, this cannot be said for certain.

Other members of the Imperial Family
Castor and Pollux rui Britannia are a pair of twin princes introduced in the Code Geass video game for Nintendo DS. Repeat playthroughs of the storyline add them as new antagonists to allow the recruitment of Cornelia and Euphemia, as well as certain other Britannian officers.
 * Castor rui Britannia
 * Pollux rui Britannia