Exit Through the Gift Shop - an amusing documentary about somebody trying to find Banksy (a street artist), and much more, supposingly directed by Banksy himself.
There is some debate if it is documentary or not (the story is almost too good), but it seems the evidence suggests it is real.
EDIT: sorry, I missed the "last 4 years" part in the question. This film is older than that.
Definitely this, my subconscious can't let go of the question as to whether this documentary is an exquisitely elaborate hoax or a rare capture of a "truth is stranger than fiction".
And if the goal was to create that confusion... meta-wow.
There is some debate if it is documentary or not (the story is almost too good), but it seems the evidence suggests it is real.
EDIT: sorry, I missed the "last 4 years" part in the question. This film is older than that.