How did Mandela die?

Did he die of natural causes or was he on life support that was switched off last night?

This comes at a rather interesting time as his movie has just been released.

I am from South Africa and it's been in the news for a very long time that he was critical and in hospital for ages. We all thought he was going to die months ago but machines were likely keeping him going.

I wonder if they waited for the movie to be released before turning of his machines or what?