Was Don Juan a murderer? (4-6)

I believe the answer is:

lady-killer

I'm a little stuck... Click here to teach me more about this clue!

'was don' is the definition.
I can't tell whether this defines the answer.

'juan a murderer?' is the wordplay.
'juan' becomes 'lady' (I am not sure about this - if you are sure you should believe this answer much more).
'a murderer?' becomes 'killer' (murderer is a kind of killer).
'lady'+'killer'='LADY-KILLER'

Can you help me to learn more?

(Other definitions for lady-killer that I've seen before include "Man who thinks he's good with the girls" , "Irresistible philanderer" , "Man irresistibly attractive to women" .)

I've seen this clue in the Sydney Morning Herald.

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.