A throne designed for someone else (7)
I believe the answer is:
another
'someone else' is the definition.
(I've seen this before)
'a throne designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'throne' is an anagram of 'nother'.
'a'+'nother'='ANOTHER'
'for' acts as a link.
(Other definitions for another that I've seen before include "On earth (anag.)" , "encore?" , "Additional: alternative" , "A further (item)" , "second" .)