After the Cambodian coup of 1970 in which Sihanouk was ousted by Lon Nol, Yuon became a part of the GRUNK, the Beijing-based government-in-exile that was formed as a coalition between Sihanouk and the communists.
Yuon's outspoken criticisms of Khmer Rouge policy led to him spending a brief period in a 're-education' camp, K6, in 1974.