For what it's worth, that was his second attempt to marry someone after he broke up with my mother. The first was with a woman who hated me in absurd levels to the point that she would attempt to choke me and throw knives at me because (according to my father, I was too young to actually engage her in any form of discussion) I reminded her of his previous relationship. And all that happened after 4 years of him being in a casual relationship with her.
Anyways, I don't know if I would call it changing or rather that there are people who try to hide their true colors until I get what they want.
May I suggest that it is highly unlikely there were no warning signs. This level of violence does not come out of nowhere (neither in women nor in men). It tends to consequence of escalations. The hate toward the offspring itself should have been seen as warning sign.
Like, yes, dad is there victim of domestic violence too. But like with women who pick yet another abuser again, there is issue with partner selection, not knowing warning signs or interpreting them as passion or some variant of that.
Admittedly, you also mention "bad at relationships" and that element was present on both sides as well.