US city taking ages to welcome English king (7)
I believe the answer is:
yonkers
'us city' is the definition.
(city in New York state)
'ages to welcome english king' is the wordplay.
'ages' becomes 'yonks' (I've seen this before).
'to welcome' means one lot of letters goes inside another (inserted letters are welcomed in).
'english king' becomes 'er' (abbreviation for Edward Rex, various English kings. I am not sure about the 'english' bit.).
'yonks' going around 'er' is 'YONKERS'.
'taking' is the link.
(Other definitions for yonkers that I've seen before include "NYC suburb" , "US city" , "American city" , "City of New York State" , "NY suburb" .)