This is a big time rumor from an unknown source. Big bucket of salt on this.
The origin story of Camelot and its inhabitants–Arthur, Lancelot, Guinevere and Galahad.
According to tracking-board.com:
Robert Pattinson has been offered one of the lead roles in the new King Arthur retelling PENDRAGON, filling in one of the spots left open after Eric Bana and Michael Fassbender dropped out of the production. Project is a reimagining of the founding of Camelot by King Arthur, with Pattinson up for the role of the fabled king. Pattinson’s potential casting projects a different light on the project, signaling a possible change in tone for the production than when Bana and Fassbender were considered for the leads.