One group of wise men and boy, it's supposed (8)
I believe the answer is:
imagined
'supposed' is the definition.
('imagine' can be a synonym of 'suppose')
'one group of wise men and boy' is the wordplay.
'one group of' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'wise men' becomes 'magi' (the three wise men from the nativity).
'and' says to put letters next to each other.
'boy' becomes 'ned'.
'i'+'magi'+'ned'='IMAGINED'
'it's' is the link.
Can you help me to learn more?
(Other definitions for imagined that I've seen before include "Created mentally" , "Conjured up in the mind" , "Visualised" , "Formed a mental picture" , "Envisaged" .)