Queen visiting for one chance to see old king (6)
I believe the answer is:
egbert
'old king' is the definition.
(I've seen this before)
'queen visiting for one chance' is the wordplay.
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'visiting' is an insertion indicator.
'for one' becomes 'eg' (both can mean 'for example').
'chance' becomes 'bet' (I've seen this in another clue).
'eg'+'bet'='egbet'
'r' going into 'egbet' is 'EGBERT'.
'to see' acts as a link.
(Other definitions for egbert that I've seen before include "The C 9 king of West Saxons" , "Old king" .)