Can you not tell him about it but then help him set up an Isa - ideally a stocks and shares one with good returns - and help him drip feed it in monthly, he can put 20k a year into it.
My DC were beneficiaries in my cousins will a couple of years ago, the payout came a couple of months after DS 18th, substantially more than 30k.
Fortunately we had spoken from the day they got the probate estimate (and thus could guestimate their share) about how lucky they were and how this would be their house deposit if managed properly.
They already had S&S ISAs that we were putting money in, I helped DS split his into bonds of 1-3 yr durations, plus a years worth of ISA money in an accessible account. He moves it from there to his current a/c monthly to cover his ISA Direct Debit.
We now have control of DDs money, she will turn 18 next year. She has some in a National savings account, the rest in the highest interest account we could get for a 16yo! I withdraw from that quarterly to again drip feed into her ISA, although she is limited to how much can go in as under 18. Once she is 18 we will do same as for DS, split between bonds etc.
Very few people know about the money, only 1 friend locally whose kids will get an inheritence at 25. She told me I was mad to tell them about the money - I didn't - they were sent a letter from my cousins solicitor days after his death!!! Plus a copy of will, probate estimate and final accounts, all addressed directly to them. And for some reason my cousin wasn't advised by solicitor to put a minimum age in will, so they got it at 18. I think, as most of beneficiaries (all cousins' DC) were older, some in 40s, it didn't occur to him.
I can understand how a lot of kids can blow it, but with ours we have gone down the route of discussion, information and proactively helping DS set up accounts. I know I would have no control if he decided to close those and blow it all, but fingers crossed he is showing no sign yet, at almost 20.