Ioan Gruffudd says that James Cameron has a 'Jekyll and Hyde' personality.
Cameron is on producing duties for new movie Sanctum, which Gruffudd stars in alongside Rhys Wakefield and Richard Roxburgh.
But the actor admits that sometime Cameron boarder on 'insanity' when on set but off set is the complete opposite.
Speaking to Digital Spay the actor said: "What is extraordinary about him is, is on set he is pretty intense - bordering on insanity sometimes, or so it seems for an outsider.
"Knowing where he is coming from, from a creative standpoint as an actor, I can see that he's just so, so passionate about getting it right.
"But then, in complete contrast off the set, he is the most charming, effervescent man you will ever meet.
"He has fantastic stories, incredible leadership qualities. It's a Jekyll and Hyde thing, really."
Gruffudd is back on the big screen later this year with Foster, which is directed by Jonathan Newman.
Sanctum is out now on DVD and Blu-Ray.
Tagged in Ioan Gruffudd James Cameron