Rejoice over Edward having become king (7)
I believe the answer is:
crowned
'become king' is the definition.
I can't judge whether this defines the answer.
'rejoice over edward' is the wordplay.
'rejoice over' becomes 'crow' (I can't justify this - if you can you should give a lot more credence to this answer).
'edward' becomes 'Ned'.
'crow'+'ned'='CROWNED'
'having' is the link.
Can you help me to learn more?
(Other definitions for crowned that I've seen before include "Installed as monarch" , "Formally made monarch" , "wreath on head" , "Invested with regal power" , "Invested as monarch" .)