German emperor in King Arthur's capital is seen by Her Majesty (6)
I believe the answer is:
kaiser
'german emperor' is the definition.
(I've seen this in another clue)
'king arthur's capital is seen by her majesty' is the wordplay.
'king' becomes 'k' (abbreviation for king in chess).
'capital' suggests taking the first letters.
'seen by' means one lot of letters go next to another.
'her majesty' becomes 'ER' (Elizabeth Regina).
The initial letter of 'arthurs' is 'a'.
'k'+'a'+'is'+'er'='KAISER'
'in' is the link.
(Other definitions for kaiser that I've seen before include "Old German emperor, pre-Hitler" , "Ruler over empire" , "Old German emperor like Bill" , "Austrian bigwig" , "Former German emperor" .)