Do I need to finish AC3 before playing this?

HI - I have taken the plunge and bought a Xbox One - and one of the games I am looking at picking up is AC4: Black Flag....

Do I need to have finished AC3 to follow the story etc in this game? - is it a direct sequel? or is it more of a game in the same AC universe?

Thanks :)

I would say yes finish AC3 as there's some things that happen in AC3 that will make alot of sense in AC4 without giving away too much, its definitely worth it :)