Old French monk? He’s involved with their tempter! (5,3,6)

I believe the answer is:

peter the hermit

'old french monk?' is the definition.
(12th-century priest)

'he's involved with their tempter' is the wordplay.
'involved with' indicates an anagram (involved can mean confusing or complex).
'their'+'tempter'='theirtempter'
'he' with its letters anagrammed with 'theirtempter' makes 'PETER THE HERMIT'.

(Another definition for peter the hermit that I've seen is " Crusade leader".)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app