Take apart Diana's cloak (9)
I believe the answer is:
dismantle
'take apart' is the definition.
(I know that take apart can be written as dismantle)
'diana's cloak' is the wordplay.
'diana's' becomes 'Di's' (Di is short for Diana).
'cloak' becomes 'mantle' (mantle is a kind of cloak).
'dis'+'mantle'='DISMANTLE'
(Other definitions for dismantle that I've seen before include "Take apart" , "Undo" , "Take to pieces" , "Pull to pieces" , "Take to bits" .)