I'm surprised to be truly engaged, always (4,1,5)
I believe the answer is:
well i never
'i'm surprised to' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'truly engaged always' is the wordplay.
'truly engaged' becomes 'wellin' (I am not sure about this - if you are sure you should believe this answer much more).
'always' becomes 'ever' (synonyms).
'wellin'+'ever'='WELL I NEVER!'
'be' is the link.
Can you help me to learn more?
(Other definitions for well i never that I've seen before include "That's hard to believe!" , "Always sick, me?" , "That surprises me!" , "The call of the malingerer" , "that comes as a great shock" .)