The Ruin of Hitler, a parting novel by Stephen (3,4)

I believe the answer is:

the liar

'novel by stephen' is the definition.
(Stephen Fry novel)

'the ruin of hitler a parting' is the wordplay.
'the ruin of' is an anagram indicator (I've seen 'the ruins of' mean this).
'parting' indicates putting letters inside (one word creates a gap in ie parts another word).
'hitler' with letters rearranged gives 'thelir'.
'thelir' placed around 'a' is 'THE LIAR'.

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.