Complex sentence: Mao Zedong later actually selected his nephew, Mao Yuanxing, as his heir, but Mao Yuanxing was promptly arrested, together with Jiang Qing, Mao's wife, soon after Mao's death.
Split into simpler sentences: Mao Zedong later actually selected his nephew, Mao Yuanxing, as his heir. However, Mao Yuanxing was promptly arrested, together with Jiang Qing, Mao's wife, soon after Mao's death.