I want to know the answer to the following question:
Who was the first non-Fujiwara emperor since the ninth century?
All the background I'm provided with is that "Go-Sanjo also established the In-no-cho (ja:院庁 Office of the Cloistered Emperor), which was held by a succession of emperors who abdicated to devote themselves to behind-the-scenes governance, or insei.". Is that enough to answer the question?