What "we" endured under the Ottomans is in part latter-day myth on top of historical facts. For example, I read a few years ago a historians' article on Ottoman military campaigns in Hungary, where they explained that contrary to general assumption, the majority of those armies weren't Turks: most were recruited (as regular army or mercenaries) near the border, that is they were Bosniaks, Serbs and Bulgarians, and not even all Muslims. This while at the same time, a lot of Serbs fled the Ottomans into what was the Kingdom of Hungary, most to Vojvodina but some going as far North as Szentendre, North of Budapest.

So there have always been people arranging themselves with the powers-that-be and those for whom the new rulers were mortal danger, and after the successful establishment of a nation state, later national mythology will always conserve only part of the whole picture.

all though he did not spear any of us Slavs in this matter

I don't know; but that he had prisoners of war executed after the final vitory (and not just Ustashi but regular soldiers) would not put it far from him.

but I have heard recently that after WWI our king did not do anything like that. All though I am not sure...

Things happened before the establishment of central authority, though central authority itself may have supported it. At the end of WWII, every force was trying to 'create facts' and grab as much territory as possible. What is now Slovenia was a flashpoint for this: the area called Lower Styria, including Maribor, was majority-German by all accounts, but Slovenian forces managed to take over. Maribor was heavily de-Germanised afterwards, most inhabitants were 'persuased' to go North. (Not that the Austrians were any better with the Slovenian minority during WWI.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}