Vassal question

[OldRanger]

Here is one that through me off. I invaded France to press my wife's (queen) claim to a dutchy. Won and she got the dutchy. A few minutes after she got it though, she became the vassal of the French king. I am also a King. Any idea what the mechanic is that produces that out come?
Thanks.

 

[yezhanquan]

The duchy you pressed for is probably a duchy belonging to Kingdom of France de jure (by law). If possible, land your wife before pressing the claim.

 

[Gingerninja]

Either of them asked to make her a vassal. Being inside BBB who has a claim on you, isn't good. The only solution would be to swear fealty. Anything else is ridiculous.
Had she been of your dynasty, you would've kept her has your own vassal, now you just have to wait till both of you die, and that France hasn't got high CA