James Wan stepped behind the camera for 'The Nun' as second unit director for Corin Hardy.

The mastermind behind 'The Conjuring' franchise - who directed the first movie and its sequel before taking on a producer role for 'Annabelle' and 'Annabelle: Creation' - helped out the filmmaker at the helm of the upcoming horror flick.

Corin told EW: ''Very excitingly, James Wan was my second unit director in a little bit of additional photography.

''It is funny, but we did some additional photography, and you're always pushing for double what you really can afford, time - or budget-wise. I said, 'I want to do all of this, but if we're going to do it, we really need to run two units.'

''James is a full-on, hands-on guy and he was like, 'Anything I can do of service!' It was like, 'I really want to take you up on that.' So, there were nights when he was shooting a section in the forest and I was shooting interiors.''

It was a fittingly scary time on set for Corin as the cast and crew shot scenes in ''a real Romanian fortress'', which left everyone feeling a little shaken.

He explained to CinemaBlend: ''Where I was situated, I had to be out of camera shot, so I was in one of these cells ... I see these two guys from the crew, probably sound department, just sort of sitting back a little further in the dark.

''I said hi. I was focused on the film. I turned my back and sat with my back to these two guys. And I was watching the monitors. Half an hour later ... I finally got the shot ... I got up and turned to the two men and said, 'Did you see that?'

''And I turned around and ... there was just no one in the room. And there hadn't been anyone in there at all. There's nowhere they could've come out of. I saw them on the way in. I just felt that they were there the whole time.''