Facts about old king with new blazer (7)
I believe the answer is:
inferno
'blazer' is the definition.
(something which 'blazes')
'facts about old king with new' is the wordplay.
'facts' becomes 'info' (I've seen this in another clue).
'about' is an insertion indicator.
'old king' becomes 'ER' (abbreviation for Edward Rex, various English kings).
'with' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'er'+'n'='ern'
'info' placed around 'ern' is 'INFERNO'.
(Other definitions for inferno that I've seen before include "Dante's work" , "Large and out-of-control fire" , "Huge fire" , "Huge conflagration" , "Large uncontrolled fire" .)