Ok. Might be bug, might not be. But there is something I noticed in my game yesterday.

I had short war with France as England. Ended in reaffirming our alliance sealed with royal marriage (of french princess to my heir).

Time goes by, France again decides to attack me. This time I kill them out, as my king is on his way to crusade (damn pope) I remember to check if he will have offspring pop out while uncomfortably far from home.

Guess what... It appears his wife dropped dead at same time her nation was defeated! Not sure if king can still remarry to get direct heir or if it goes sideways to his brother but it is bit odd in my opinion for queen to kick the bucket in such situation.