Which bead for a external corner.. Only 1 side skimmed???

[Rapture]

Hi,

After some advice please. My fireplace recess has been lined with glasroc ready for a stove, but im unsure how the external corners are to be finished.
The inside of the recess is to be painted but the face of the breast is to be skimmed. Which bead would be the correct type? I thought a flat skim bead but someone else said a corner bead? Was confused by this as the corner bead would still be visable in the recess which is to be painted.

Thanks