Prince Naohito was the founder of the Imperial princely line of Kan'in-no-miya.
After the reigning emperor died in 1779 with no heir, his successor was taken from Naohito's line. The Heisei Emperor is thus a direct descendant, eight generations down, of Naohito.
References
- Arai Hakuseki, Joyce Ackroyd (trans.), Told Round a Brushwood Fire, University of Tokyo Press (1979), 288n22, n23.