Tadaoki had his fourth son Tatsutaka HOSOKAWA live in the main keep of Yatsushiro Castle and seemed to desire him to inherit the retirement gratuity of 95,000 koku and establish his own domain, but he died young in May 1645 and Tadaoki followed him in January 18, 1646.
忠興は四男の細川立孝を八代城本丸に住まわせ、いずれ自分の隠居料9万5千石を継がせて立藩させることを望んでいたようだが、正保2年（1645年)閏5月に立孝は若くして没し、忠興も同年12月2日に没した。