Tune heard by child - he's with man taken in by the future monarch (4,2,3,6)

'tune heard' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'child he's with man taken in by the future monarch' is the wordplay.
I cannot really understand how this works, but
'child' could be 'tot' (term for a young child) and 'tot' is present in the answer.
'man' could be 'ron' (short for Ronald) and 'ron' is found within the answer.
an anagram of 'the' is 'het' which is present in the answer.
'monarch' could be 'r' (abbreviation of Latin rex) and 'r' is located in the answer.
'he' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

'by' acts as a link.

Can you help me to learn more?