Emperor, China's last, is hosted by king and queen (6)
I believe the answer is:
kaiser
'emperor' is the definition.
(German term for emperor)
'china's last is hosted by king and queen' is the wordplay.
'last' indicates one should take the final letters.
'hosted by' indicates putting letters inside.
'king' becomes 'k' (abbreviation for king in chess).
'and' means one lot of letters go next to another.
'queen' becomes 'ER' (short for Elizabeth Regina ie Queen Elizabeth).
The final letter of 'china' is 'a'.
'a'+'is'='ais'
'k'+'er'='ker'
'ais' put inside 'ker' is 'KAISER'.
(Other definitions for kaiser that I've seen before include "Old German emperor like Bill" , "Austrian bigwig" , "Ex-ruler of Germany" , "Ruler over empire" , "Emperor of Austria or Germany until 1918" .)