We all know that TV shows and movies exist in their own, constructed universes.
But sometimes, worlds collide. So tell us: what's your favourite fictional universe crossover?
Do you love the fact that in Friends, phoebe's evil twin Ursula is a real character from Mad About You?
Perhaps your favourite episode of Brooklyn Nine-Nine was when Jess from New Girl showed up.
Or maybe you still can't get over the time that The Simpsons and Family Guy's worlds collided.
