User blog comment:Ḡwẵine Ḹٍٍkƨ Ĺiĸe Ͼềлȑềd/WORST plot hole in the HISTORY of 'Merlin'/@comment-4623180-20121014122211

Hmm... he really did forget. I mean, all Mordred said was "you saved my life, long ago". Arthur has saved many lives, though.

Also Arthur only heard Mordred's name said once, "Mordred", and this was eight years ago...

Maybe some of those injuries over time caused some memory loss... nonetheless he really has completely forgotten....