Tan's younger brother was Kijuro SHIDEHARA, a politician who was a diplomatic, and Kijuro's wife, Masako, was the fourth daughter of Yataro IWASAKI, the founder of Mitsubishi Zaibatsu (a financial clique or group, or company syndicate).
坦の弟は外交官出身の政治家・幣原喜重郎で、喜重郎の妻・雅子は三菱財閥の創始者・岩崎弥太郎の四女である。