According to "Hone wa kataru tokugawa shogun daimyo-ke no hitobito" (bones tell stories; the people of the Tokugawa clan and the daimyo family), written by Hisashi SUZUKI who attended the refurbishment of the Tokugawa Shogun family's graves at Zojo-ji Temple where Ietsugu was buried to examine the cremains of the buried, when Ietsugu's coffin was opened, the rain water for many years were in the coffin and his bones were not in it; there were just his hair, nails, and articles such as his swords.
家継の埋葬された増上寺で徳川将軍家の墓地が改装された際に、これに立ち会い、被葬者の遺骨の調査を行った、鈴木尚の著書『骨は語る徳川将軍・大名家の人びと』によれば、家継の棺を開けた時、長年の雨水が棺の中に入り込み、家継の遺骨は存在せず、ただ家継のものと思われる遺髪と爪、及び刀等の遺品があったのみであったという。