This section contains spoilers for: Dragon Age: The Calling.
Kell claims that Hafter had also ingested the darkspawn blood during the Joining ritual of the Grey Wardens, making him one of that order as well as immune to the darkspawn taint.
When Kell sacrifices himself to save King Maric, Fiona and Duncan, Hafter does not want to let him go alone. Kell does all he can to make Hafter stay with the rest of the party, but the hound does not listen and goes to the final battle with his master. It is suspected that both of them died in Kul-Baras.