2nd hand phone but still connected to an apple ID

I have an old iphone 5c that I'm passing onto a friend. I thought it was all reset, but when I gave it to them it was asking to login to an apple ID. I've checked and both my apple ID doesn't have this phone attached to it. However, it's saying that it's needed to reset the phone. It says login to apple ID c••••••@icloud.com I have never had an apple ID that starts with 'c'.

What can I do?

Any help would be much appreciated.