Hesitantly wonder why Lord Gernert had to be killed once he'd been disarmed.
Suggest that some of House Gernert's territories go to [Your House].
Subtly remind Lord Frey that it is [Your House] he owes his gratitude.
"Pah!" Walder Frey dismisses Eutimio. "Donnel asked what to do with the body. I told him to throw it to the dogs. The final resting place for traitors."
Eutimio kneels before Walder Frey at Riverrun. "Ser Donnel tells me we have you to thank for our victory. He says you showed unmatched loyalty."
"What House Gernert?" Walder Frey laughs spitefully. "Thistledowns'll go to Donnel. All the sons I have, I need every castle."