ROYALE 400

I believe it is locktite and requires heat to break the bond. Airgun Nation User jking can tell you because he has one and I think he did remove the moderator on an occasion for troubleshooting purposes.

Thurmond

http://www.fxairguns.com/wp-content/uploads/2015/10/Royal-Drawing-and-Partlist.pdf

You'll need a source of heat to break the adhesive free. 
Remove the end cap, heat up the breech side of the tube (remove or protect your bottle) where parts A-3 and A-4 meet. The Royale should be a slide on so, keep trying to twist and pull while applying the heat. That should slide off. It might get caught on part C-3. C-3 is also lock-tited in place. Add heat and unscrew. Use something (like a pencil) to give you leverage but not damage anything. The other end of the shroud is simply held in place with an allen screw. 
Take you time. If something starts to "not feel right" during the process, come back on here and ask. 
Best of luck! 
Tom

This is excactly what I did to get the moderator off my Royale 500. I used a Butane torch for the heat source. Worked very well. 

This is excactly what I did to get the moderator off my Royale 500. I used a Butane torch for the heat source. Worked very well. You need to apply quite a bit of heat though to melt the locktite, so keep the heat on it (won't damage the moderator) and twist/pull as you do it. And yes, do cover the air bottle with aluminum foil. Don't want to heat that up!!!!

I took the moderator off my Royale 500 and used no heat whatsoever. It just unscrewed (A-3 and A-4 in the diagram).

I did not try taking C-3/4 apart.