Treated thus, get partner Peter Grant (10)
I believe the answer is:
anagrammed
'treated' is the definition.
Although both the answer and definition are past participle verbs, I can't see how one could define the other.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for anagrammed that I've seen before include "made quite quiet, for example" , "Moved around" .)