
Reaction to what exactly? If you're asking about his reation to Judith and Luca's regression, he's not that surprised since he was already expecting that the two were hiding something from him. If it's about the thing about the stuff about Jonas, he was surprised at first, specially after knowing that the duke was the one who killed Jonas. But after that, he became calm again? He didn't really show much violent reaction. At least that's how I read it. It was MTL so some nuance might have been lost on me.

With Judith being a royalty. They actually become parents to Luca just like our Rui wanted in the initial chapters ε=ε=(ノ≧∇≦)ノ
The former king finally feels remorse and the false claims of Father Winterwalt killing Vanessa is resolved but this would also mean them finding out he killed Jonas ┗( T﹏T )┛
So I got curious and went ahead and read the novel. This part here is around chapter 130+. Anyways, the guy who saw Luca in this chapter was named Max. He has a daughter named Chloe who's sick. He's doing this because he needed money to cure her. Judith managed to convince him to turn against Franz by offering him more money.
Judith and Luca were about to escape but Franz returned much earlier because Rudieger and his soldiers were closing in on the place. With Max's help, Judith and Luca were able to hide in some room. Max sacrificed himself to save the two but not before Judith makes a promise to help his sick daughter.
Franz still managed to find them tho. He was about to kill Judith since he couldn't have her but shooting at her, but Luca tackled him so the bullet's trajectory changed. It still grazed Judith's side tho. But no one noticed until Ruediger arrived and shot Franz. When they saw that Judith was bleeding, Ruediger thought that she was hit by the bullet he shot. This man legit gonna off himself if Luca hadn't stopped him.
Don't worry, Judith is fine. She woke up a few days later. Ruediger didn't leave her side and was crying the whole time. It was in this scene that Judith and Luca talked about their regression. Yes, apparently, Judith is the real Judith and the novel that he thought she read were just memories of Luca. She didn't hate Luca and was just very hurt and angry because of what happened to Larissa (Luca's mom). So he vowed revenge towards the Winterwalds in their past life and joined hands with Franz. But when she found out that Franz was trying to kill Luca , she tried to stop it but was killed by Franz instead. Then the two finally remembered that Ruediger in in the same room.
Luca said here that he wouldn't take the Winterwald name because he's not a real Winterwald. Apparently Jonas was the son of princess Vanessa with another man. Which the current duke of Winterwald confirmed when he visited and talked to them.
Son the princess felt so suffocated because of the former king that she lived a secret debauched life as a retaliation. But she got pregnant. So she asked the current duke of Winterwald to make deal with her. She knew that the duke loves her maid. She said that if she married her and took in the child she's bearing, she would fake her death and he could marry Sophia (Ruediger's mother) after. But she died of childbirth so.
The duke also really killed Jonas. It's because this guy planned to be the bext king by wishing on the magic cup that the heads of the Winterwald see after they became the head. It's also the cup that help Luca and Judith regressed because Luca wished to be happy. And Jonas also said that the first thing he would do once he became the duke was to kill Sophia. Because she's just a lowly maid who took his mother's position, not knowing that his real father was just some random guy.
Anyways, the former king finally approved the marriage and the two got married.
I'm kind of tired typing, so if you have any other question, just asked. Lol.