Probably something trendy listed in a baby name book- my mom went for that nonsense with both my brother's and my original name. I had 5 people in my graduating class that had my same name, and it wasn't a common name that sticks around over the years.
Or - I could have been (family name) IV ... I thought about doing that when I changed my name but figured it was not my place, and I don't talk to my parents and they don't know about my transition, so I couldn't ask them.