As at first, Henry VIII was intellectual (8)
I believe the answer is:
thinking
'intellectual' is the definition.
(thesaurus)
'as at first henry viii' is the wordplay.
I cannot quite see how this works, but
'at' could be 'in' and 'in' is found within the answer.
'first' could be 'i' (I in Roman numerals eg Elizabeth I) and 'i' is present in the answer.
'henry' could be 'h' (symbol for the unit of electrical inductance) and 'h' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'was' acts as a link.
(Other definitions for thinking that I've seen before include "Fancying" , "giving opinion" , "Thought" , "Mental process" , "Pondering" .)