Card learner turned over gave the game away (3,2)
I believe the answer is:
let on
'gave the game away' is the definition.
(to let on is to give a secret away)
'card learner turned over' is the wordplay.
I cannot really understand how this works, but
'learner' could be 'l' (as in a learner driver with L-plates on their car) and 'l' is found within the answer.
'over' could be 'on' (physically on top of) and 'on' is present 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 let on that I've seen before include "Pretend informally or permit to board" , "Divulge (secret to)" , "Be revealing" , "Spill the beans" , "give the game away" .)