Sorry to hear about that mate.
My big brother passed away 4 weeks ago, he didn`t smoke, he didn`t drink much, he was fairly healthy living and keeled over with a massive heart attack at the age of 55.
When someone close leaves us out of the blue like that it`s a massive shock to system, keep fighting, celebrate what they brought to your life, celebrate their life, remember the good times and stay strong mate.
I feel your pain.