Regal crest pants worn by Prince Edward (8)
I believe the answer is:
sceptred
'regal' is the definition.
(I've seen this before)
'crest pants worn by prince edward' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'worn by' indicates putting letters inside (outside letters are worn by those on the inside).
'prince' becomes 'p' (abbreviation for prince).
'edward' becomes 'Ed' (short for Edward).
'crest' with letters rearranged gives 'scetr'.
'scetr' placed around 'p' is 'sceptr'.
'sceptr'+'ed'='SCEPTRED'
(Other definitions for sceptred that I've seen before include "showing sign of authority?" , "Regal" , "Like our isle" , "This -- isle (Richard II)" .)