We do intend to return someday... and Rosenkreuz is a man of opportunity. Perhaps it's something as simple as taking advantage of our current entrapment to gain at least some favor with me. Having the king not exactly fond of you can make one's life a bit difficult.

[When one has their king in the same situation as them, it makes sense to try to get him on your side. And admittedly, Henry is already somewhat fond of Rosenkreuz, in a way.]

For now, if nothing else, we all fight under the same banner. I certainly won't look down on any help in this situation.