I would phone his parents. Say that you have heard he has died and ask them to confirm it. If he has, offer sympathy and have a chat with them, discussing memories etc.
If he hasn't died and it's just a rumour, they may well have heard it and share the 'joke' with you.
You may be surprised to know that part of the healing process for those left behind following a death is to be able to talk about it. His parents will want to be talking to people who new him. That will be so important to them. We all find it difficult to find the right words in this situation but we should say something. Silence just adds to the heartbreak.
Speak to them. You'll be glad you did, and they'll be glad you did.
Stay silent and you may regret it for ever.