Apparently Kurtan's nan (with the pixellated face) is a A list actor who flew in specially to do it. They are not saying who it was but have given some clues eg not from England, has a very creative partner, they had never met this person before
I saw this but I don’t think they will ever reveal who it was unless someone leaks it. They were both on a podcast I listened to where they said they wouldn’t reveal who it was and no one would ever guess. so who knows
Major major props to Paul Chahidi who plays the Vicar he is absolutely spot on casting and the three of them together are such a joy to watch.