Quickest collapse you've seen?

[The Unknown Guy]

I don´t remember reading that in the manual. I thought it only applied to "Generals of Royal Blood" AKA: former princes out of the succession line. Which I know to take place not for personal experience, but because I murdered several "heirless" kings of Sicily, and some remaining "royal knights" became kings over and over. In fact, I had to çuit my friendly face and invade them straight off, instead of just buying off Malta.

[Martok]

The Unknown Guy is correct. The manual only mentions "princes of the blood" as being able to ascend to the throne (and that a civil war is still possible even if that happens).

These gentlemen are usually the dead king's uncles (and in rare cases, great-uncles), and you'll always be able to recognize them: They'll appear as regular generals, except that they'll also have a crown on their info parchment, indicating the man is of royal blood. To the best of my knowledge -- and my experience reflects this as well -- they're the only generals that can become king if your faction leader dies without a direct heir.