Merlin's guide on how to tell Arthur you have magic.
Save his life once or twice
Become his Man servent
Save his life some more
Do some magic behind his back
Do some magic right in front of him but he still doesnt realise, because he's such a clot pole
Do all of your chores at the same time by using magic
(You would think arthur would be suspicious by now..)
Wait until Arthur is king
Save his life some more by fighting Morgana
say "there is no place for magic in Camelot"
Get fed of lying to him, tell him you have magic and hope for the best.