Solving "rightful liege"

[Jaboleon]

I'm continued the tutorial, and I have taken Connacht by force.

The game states, via tutorial pop up along the top, that I am not the rightful liege.
I'm just not understanding the tool tip nor do I follow it well.
How do I solve this?

[Fastmine[NOR]]

If you have a county that would De Jure belong in another characters duchy, then you are not their rightful liege in De Jure terms.

[♠.brT]

The way to solve it to create or usurp the duchy that the county belongs to.

[Nathan]

Basically because you're not their De Jure liege (because by tradition the Earl of Connacht should be vassal to the Duke of Connacht) you get a slight penalty for being the overlord of that county. However, this is fairly easy to solve.

You just need to become the De Jure lord of the county. This basically means, take the other county in the duchy - Briefne I believe - and form or usurp the Duchy of Connacht. You should be doing this any way as you need to hold two duchy titles in order to form the Kingdom of Ireland.