Seemingly, he must succeed (4,8)
I believe the answer is:
heir apparent
'seemingly he must succeed' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'seemingly he' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'ira' and 'ira' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for heir apparent that I've seen before include "Next in line to throne" , "successor eventually" , "One expected to succeed" , "sure of inheritance" , "Acknowledged beneficiary" .)