glioblastoma multiforme

im new in here and i have been searching the internet for a forum that deals with loved ones cancer,we just got told last tuesday 3rd march 2009 that my sons dad has terminal cancer of the brain,his doctor said he was lucky as most people with this cancer don't manage to live past 2 years or so,he has now had it for alittle over 4 years....we split up whan our son was 4 years old but have remained firm friends... he never told me the extent of his tumour! i learnt this all last week.so as you can imagine this has come as a shock! we talked about it and he decided that he didnt want anyone to know (i guess he needs to handle this himself first) but we do have a 16 year old son that doesnt know anything except his dad "had" a tumour (not "got" a tumour) and will probly not see his own birthday in june..he has glioblastoma multiforme....his doctor explianed that he was lucky to get a second operation on this as they dont normally do it,but recent scans revealed that it has changed shape again and there is no surviving it....i guess my first question has got to be "would you tell your child as early as possible?or would you wait a few weeks/months?" (i wouldnt know how to tell him but i would find a way as gently as i could) second question is "i have know idea what to expect in the coming weeks/months on how he (sons dad) is going to be towards the end,ive read blogs but they dont really tell me much,i know each case is different but any insight would be appreciated