Removing a device from Find iPhone

I used to have both my phone and somebody else's registered on my Find iPhone in my iTunes account. That person and I have since parted ways on bad terms. I changed my passwords to make sure that person cannot temper with my account. That person's phone, however, has stayed in Find iPhone for me to see. I tried to remove it (only possible when it is turned off), but it reappeared.

The only option I seem have is to remotely erase the iPhone. Will the other person have any means to see that I remotely deleted it? Or will it just be erased? Follow-up: If they restore from backup, will they appear in Find iPhone again? I need a way to get rid of that phone from my account.

Disclaimer: I do not, under any circumstances, want to talk to that person.

Remotely wiping a device, as long as you don't set a lock screen message, will look just like a regular wipe of the phone. However, the person with the phone will have to enter your Apple ID password to use it again.

The reason the phone keeps showing up on Find My iPhone is that your Apple ID is still on the phone, to remove it, all you need to do is wipe it then select remove from account. The person with the phone will not need to enter your password to use it again.