At the end of Fatman and Robin, the camera pans up to Stewie on the roof, with him saying "I guess Disney wouldn't let us do the Aladdin one." In reality, Robin Williams had a falling out with Disney over the genie character, and did not allow anyone to use the character's likeness.
This episode, where everyone (and everything) Peter touches turns into Robin Williams finished airing on BBC3 minutes before news broke out of the actor's suicide.
When the queen dies in a tunnel it's a reference to princess Diana's death
Brian (as a horse) say "hwim" the same way that Stewie normally says "hwip."
Calling a Royal a "Wanker" is technically Sedition.