Cor's not going to apologize for punching Clarus, not in that moment. Maybe the next morning, though, he might say sorry for losing his temper that badly.

The confirmation of Regis' killer, however, only stokes the anger inside Cor, fists clenching at his side until the knuckles turn white. But there's some guilt mixed in with his fury. Guilt of not realizing it sooner, or being closer to the battles that Drautos--Glauca was involved in, so that he could've stopped him then...

Still, hearing that the traitor was killed that night does reduce his fury back down to 'can think thru it' levels. "...at least there was one Glaive that remained loyal to the end," he quietly grumbles.