Matsudaira also participated in meetings with newly elected kazoku managed by Fumimaro Konoe, Kōichi Kido and Kumao Harada associated with Jūichi-kai (十一会).

[4] He retired from that position on 24 November 1945, and on 17 January 1946, he assumed the presidency of the Bureau of Peerage until it was abolished in 1947.

Matsudaira was one of the central aides of Hirohito and the Imperial House of Japan, and after the end of World War II, he contacted the Supreme Commander for the Allied Powers and testified against the International Military Tribunal for the Far East.

[5] From March to April 1946, he comprised the Go-jin no kai (五人の会) with Matsudaira Yoshitami, Hidenari Terasaki, Inada Syūichi and Michio Kinoshita, and interviewed the Emperor while writing Shōwa-tennō dokuhaku-roku (昭和天皇独白録, Shōwa-tennō dokuhaku-roku).

"[6][7] On 27 March 1947, Matsudaira assumed his position as the Grand Master of the Ceremonies.