By being soft on royalty (3)
I believe the answer is:
per
'by' is the definition.
(thesaurus)
'soft on royalty' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'on' is a charade indicator (letters next to each other).
'royalty' becomes 'er' (abbreviation for Elizabeth Regina).
'p'+'er'='PER'
'being' acts as a link.
(Other definitions for per that I've seen before include "According to" , "Preposition meaning for each" , "For each or every" , "Preposition indicating by means of" .)