Bigshot meeting the queen is traitor (5)
I believe the answer is:
viper
'is traitor' is the definition.
(viper can mean a treacherous person)
'bigshot meeting the queen' is the wordplay.
'bigshot' becomes 'vip' (abbreviation for very important person).
'meeting' is a charade indicator (letters next to each other).
'the queen' becomes 'er' (Elizabeth Regina).
'vip'+'er'='VIPER'
(Other definitions for viper that I've seen before include "Adder" , "poisonous type" , "Malicious person" , "Malicious type" , "Deadly-venomous snake" .)