Father's heir has one temper (7)
I believe the answer is:
Here is my best explanation:
'temper' is the definition.
'father's heir has one' is the subsidiary indication.
'father's' becomes 'pas' (pa is a kind of father).
'heir' becomes 'son' (I've seen this before).
'has' is an insertion indicator.
'one' becomes 'i' (roman numeral).
'son' going around 'i' is 'sion'.
(Other definitions for passion that I've seen before include "Intense enthusiasm for something", "Rage", "Strong emotion, anger or love", "Ardour, fervour", "Fervent love", "Ardent love", "Enthusiasm", "Ardent emotion", "Intense emotion, anger or love" and "A strong emotion".)