One of a kind
Example:
"Wow, that's a special ring! Your 'fiancèe' is a special lady,"
"Yeah, it's custom-made. I wanted to make it one of a kind, just like her."
"Wow, that's a special ring! Your 'fiancèe' is a special lady,"
"Yeah, it's custom-made. I wanted to make it one of a kind, just like her."