Article seized by charming old king (6)
I believe the answer is:
canute
'old king' is the definition.
(medieval Danish king)
'article seized by charming' is the wordplay.
'article' becomes 'an' (English indefinite article).
'seized by' indicates putting letters inside.
'charming' becomes 'cute' (I've seen this in other clues).
'an' inserted into 'cute' is 'CANUTE'.
(Other definitions for canute that I've seen before include "English king who ordered waves to retreat" , "The king who thought he could hold back the tide" , "Ancient King who commanded the tide to retreat" , "Danish King of England, 1016-35" , "English king who tried to command the waves" .)