Support the Queen, as is right (6)
I believe the answer is:
proper
'is right' is the definition.
('proper' can be a synonym of 'right')
'support the queen' is the wordplay.
'support' becomes 'prop' (prop is a kind of support).
'the queen' becomes 'er' (Elizabeth Regina).
'prop'+'er'='PROPER'
'as' is the link.
(Other definitions for proper that I've seen before include "Real; genuine" , "Suitable or appropriate" , "Genuine; suitable" , "Befitting" , "Fit; accurate; decent" .)