It would come from an unlikely source; Cherny. Written in Cherny's careful hand, and delivered by Cherny's hand as well, a wordless handing of a note, as if Elliot were a school-child or a secret love and Cherny the hapless in-between.
Ser Elliot,
I have heard that you have hurt Miss Niall very Fiercely. I know that I've said I would be your friend. But you are a Very Cruel Boy and I cannot be friends with Cruel Things because you might decide that I am a Witch and try to hurt me badly, too. I hate you quite a lot and I hope Rhaena eats your tongue.
If you say Ser Eater is a Witch and Hurt Him I will put you in a hole so deep that not even weeping Tears or Blood will bring you Out of it. I will paint a Fence with your Bones.
Love,
Catch