Sorry to tell you but there's nothing we can do about it. Once it has been transferred there's no way for you to reverse it back. It's your fault, maybe you signed up from airdrop or something. Heads up, if you're going to use MEW make sure that you don't put all your ETH and altcoins in the same wallet.
Even he signed up on airdrops it can't happen that easy!
Rule number one! never give or put your private keys on any forms over the internet.
If he did this then he is not robbed by a hacker but he made a mistakes. This can't be recovered as long as there is no identity to be know.
If the address were under KYC then there will be a possibility.
