Gave off energy, keeping Anne’s successor in pain (8)
I believe the answer is:
aggrieve
'pain' is the definition.
(I've seen this before)
'gave off energy keeping anne's successor' is the wordplay.
'off' indicates anagramming the letters.
'energy' becomes 'e' (physics symbol as in E=mcr).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'anne's successor' becomes 'gri' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gave' with letters rearranged gives '[gave]'.
'[gave]'+'e'='ageve'
'ageve' enclosing 'gri' is 'AGGRIEVE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for aggrieve that I've seen before include "Pain or injure" , "Cause to feel sorrow" , "Distress, afflict" , "Press heavily upon; distress" , "Cause annoyance to" .)