Hey James! It was the same as any other YC application :) the process is the same for everyone.
- open application that anyone can submit
- get an interview or don't get one
- if you get the interview, you get 10 min to chat
They did ask me why I didn't have a cofounder and I told them the reason. The reason being that I wasn't close enough with anyone that was passionate about the same idea and was available to do a startup.