Legendary knight's son held after Irish social event (3,7)
I believe the answer is:
sir galahad
'legendary knight's' is the definition.
'Sir Galahad' can be an answer for 'knight's' (thesaurus). I am not sure about the 'legendary' bit.
'son held after irish social event' is the wordplay.
I cannot quite see how this works, but
'son' could be 'galahad' (I have seen 'Son of 9 ' mean 'galahad' so perhaps 'son' could also mean 'galahad') and 'galahad' is present in the answer.
'irish' could be 'ir' (abbreviation) and 'ir' is present in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sir galahad that I've seen before include "paragon of virtue" , "painting by symbolist Watts" .)