When a nightmare becomes a reality.

I've sat here now for about 15 minutes just trying to think what I should write...
Last week we took on the responsibility babysitting the pet rabbit of some very good freinds of ours. Today that rabbit died. Right now I just feel at a loss about what to do. How do you tell someone that their beloved pethas died. Not to mention that Purnama was practically human. Rabbits don't usually craze such affection from people like this one did. He would follow you around the house, jump up and sit with you on the sofa and let you massage his ears for hours on end.
Yesterday was just like any other day Purnama was jumping around and being highly social and cheeky as always. Last night though he was a little on the quiet side. We also noticed that his pooh was a little more moist than usual. His owners had said before that he has had dihorrea if he ate too many vegetables. Yesterday he hadsome brocolli, so we thought it must have been that. This morning however Purnama was much more quiet than normal and he wasn't eating. He was still drinking however and od advice it appeared that although he may be feeling a little off, given a couple of days he would be good a new.
I asked Greg to go home and check on him at lunch time and if he wasn't looking better that we should take him to the vet. Greg did go home and check on him at lunchtime and decided there had been little change, so he made an appointment for 3pm today to see the vet. He went back to work for a couple of hours and then home again at 2.30pm - when he got there things had taken a turn for the worse and so he quickly rushed Purnama to the vet, but it was too late.
We've buried him in a nice spot - a place he would have liked.
Now however we're left with the guilt of feeling like we did something wrong, but I just can't think what. I've been around animals all my life and I've never had this happen. The worst thing is we'll just never know. Now we have the task of telling his owners what's happened. This is a task I can't even bare the thought of. All that is ringing through my head is Emmanuel saying "He's just like our child" - it's that thought that is making me feel sick. I just hope we don't lose our good friends over this and they know in their heart we would never have done anything to hurt their little boy.