That is sad but now action must be taken anyway. Why did this fish get sick? Can you fix the cause of the problem/death? As you now have plenty of other fish at risk!
No offence but you sound like a newbie to this as we were all once
Could you please give us more information on your tank, your fish, your tank maintenance, what you feed them, your filter, etc. This fish probably could have survived though it's not your fault but I'm sure you don't want your others to die.