Which we learn from Stan Collymore of all people:

More details as they emerge…

UPDATE: Looks legit. Sky Sports go balls deep on it:

Sky Sports sources understand that Pep Guardiola has told Barcelona he will leave the club at the end of the season.

[...]

A joint press conference will be held by Guardiola and Barcelona president Sandro Rosell on Friday morning at 11am.

So, to replace him. Marcelo Bielsa? Luis Enrique? Let the mad, useless speculation begin!

UPDATE II:

This means this story is both true and not true, if you know what I mean.

And Sid Lowe with an interesting observation: