Task: Sentence Expansion
Input (English): He has been on the Chrysanthemum Throne since his father Akihito abdicated in 2019 .
Output (English): He acceded to the Chrysanthemum Throne upon the abdication of his father , the now-Emperor Emeritus Akihito on 1 May 2019 at 00:00 local time ( 15:00 UTC ) .