I saw my daughter's friends topless

I've obviously known her for years and she regularly stays over. Last night she stayed over and slept in the guest bedroom. I'll be honest I thought she had gone home by the morning because when I woke up I walked into the bathroom, opened the door and she was standing there in just panties. She screamed and tried to cover up but it was too late, I'd already seen her beautiful 18 year old tits and I will never forget what they look like