Cheers guys I thought as much, i'll break it to him gently that it's gone for good.
This is the only option left for you to just go and tell him that no one can help you with recovering your bitcoin as private keys are main to rebuild the wallet and use your bitcoins. Just forget and move forward in life.
I have a similar story without the happy end. A friend of mine remind that he bought 20 BTC years ago just for fun and forgot about it, he remind about it one evening when I was talking about Bitcoin and what success it reached, and he was like: "hey man, I have some, but I don't even remember where it is blah blah"