Jointing villaboard to gyproc?

I am about to panel the side of my bath prior to tiling. I am going to use 6mm villaboard as this will allow space 'under the lip' of the bath rim to get the tiles in.
The bathroom walls are boarded in Gyproc aquacheck which will meet the villaboard at the wall/bath frame internal 90 degree angle.
My questions are:
1. with what/ how do I joint the internal angle from villa to plaster board?
2. Do I need to joint the external 90 degree angle on the corner of the bath panel villa board?
I hope this makes sense!
I have never actually used villa board before so if I'm missing something really obvious please just humour me!

Well, what I did in exactly the same situation was to not joint it at all. The waterproofer put tape on the all the joins including where the villaboard meets the wall (Aquacheck - same as you) so that the membrane can flex without cracking. You need to waterproof it anyway before tiling.

if no joint then you need to use a very flexible membrane - one of the polyurethane rubber ones instead of the acrylic I think. I've used a length of 45mm pvc angle in your siutation when I installed my bath so that it was behind the board on both corners. If you can no longer get behind, then you could easily set with plasterers tape and joint cement as a base for the waterporoofing membrane.

Final option is to just use the pvc flexible angle on the internal side, for noth the internal angle & the external angle, as tiles will cover and aesily absorb the 1mm thickness of the angle. tiling glue is great for making right all manor of shoddy workmanship ;D !

Just tape the internal with paper tape.

thanks for the tips gentlemen, paper tape it is...