Very keen about Queen using a towel (6)
I believe the answer is:
drying
'using a towel' is the definition.
(drying off with a towel)
'very keen about queen' is the wordplay.
'very keen' becomes 'dying' (dying for something means being very keen for it).
'about' means one lot of letters goes inside another.
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'dying' placed around 'r' is 'DRYING'.
(Other definitions for drying that I've seen before include "Airing" , "(Of actor) forgetting one's lines" , "wilting" , "Dehydrating" , "Desiccating" .)