Okay. This is pretty amazing ... Arian Foster's home security cams were rolling while he was watching "Game of Thrones" on Sunday ... and his reaction to the ending is AMAZING!!!!

Second warning ... here comes a spoiler!!!

The ex-NFL star was watching the Battle of Winterfell on his couch with some friends -- when he jumped up for Bran's final showdown with the Night King.

Third and final warning ... big spoiler coming your way!!!!

So, when Arya came out of nowhere LIKE A BOSS to stab that bitch-ass, ice-faced demon, Foster went crazy!!!!

You gotta watch the video ... Foster lets a scream you can hear -- even though the video has no sound!!!

Arian's buddy starts to dance on the couch ... even the dog gets fired up!

But now, everyone's gotta chill ... Jon Snow, Daenerys, Tyrion, Sansa and the rest of the gang have another battle on their hands next week ...

Cersei is waiting!!!!!