A couple family parties ago, my ten year old cousin and I were talking birthdays. It had just been her older brother's birthday and we were trying to figure out whose birthday was next. We eventually figured out that my birthday was next and she was the next after that, June 1st.

At the shower today, people were talking about something happening next Sunday, but I didn't catch what it was. As we were driving away, I asked my mother what was going on next Sunday. She said there is going to be a combination Memorial Day slash birthday party for my cousin and someone else but the someone else didn't register with me. Eventually it hit me that my mother had said someone else's name as well as my cousin's. As we were driving, I was trying to figure out who the other person was. Who else has a birthday around now?
It was bugging me.

Then I remembered.

My cousin has a twin brother.