Throughout the TV version of "Queen Charlotte," we see George and Charlotte's dedicated right-hand men, Reynolds and Brimsley, engaging in an affair of their own. It's mostly kept to the sidelines, and we don't know much about it other than how their relationship conflicts with their loyalties to their respective royal bosses.
Thanks to book chapters from Brimsley's perspective, we get to see the romance unfold in more detail. It starts out, apparently, as something similar to George and Charlotte: a little hostile, but also wildly attracted to each other. In time, they become more emotionally involved, to the point where Reynolds even reveals how he became George's aide: they grew up together, were each other's only friends, and knew each other's secrets. Near the end, George and Charlotte actually spot Brimsley and Reynolds dancing and are happy for them (in the TV version, we only see the two men dancing, not the royal couple noticing them).