Laurence Fox (Lord Palmerston) is the son of actor James Fox, who played Palmerston in the Danish TV mini-series 1864 (2014).
Nicholas Audsley who plays Lord Charles Monmouth and Vincent Regan who plays Louis Philippe were in The White Princess about Elizabeth of York and Henry VII. Regan played Henry's uncle Jasper Tudor and Audsley played Henry's step brother Lord Strange.
Vincent Regan, who plays the French king, Louis Philippe in series three (replacing Bruno Wolkowitch from series two), played a fictional English king in the E! series The Royals (2015).
At 06:02 minutes into the episode when Lord Palmerston and Lord Russel are getting into the carriage, Palmerston is sitting on the left and Russell on the right. At 06:50 when the carriage arrives at the palace and they begin to exit the carriage their seating positions have been switched.