I thought 'UnSouled' would come in at around 400 pages, but...

I thought 'UnSouled' would come in at around 400 pages, but it took 650 pages, and even then I felt like I was rushing the conclusion, so I asked my editor and publisher if I could divide it again. So a sequel became a trilogy, and the trilogy became a tetralogy - although we're not calling it that.