The Sino–DPRK relationship had often been described, at least until the end of the Cold War, as one of “lips and teeth” or “blood‐cemented” brothers. However, remarkable changes in the previously strong Sino–DPRK relations have been observed in recent years. Most importantly, the DPRK has ignored the People's Republic of China's repeated warnings to withhold nuclear tests, instead conducting them five times in a row since 2006. In response to those tests, China has vehemently criticized the DPRK. In addition, it voted for UN Security Council resolutions that imposed strict sanctions on Pyongyang. China even imposed its own sanctions against the DPRK. The strained relationship between China and North Korea is demonstrated by the fact that China's new president, Xi Jinping, has met South Korea's President Park Geun‐hye eight times since he came to office in 2013, whereas he has never had a summit meeting with North Korea's new leader, Kim Jong‐un, who succeeded his father, Kim Jong‐il, in 2011. What has driven this dramatic change in the relationships of these two military allies? This paper argues that while multiple factors have pushed formerly strong Sino–DPRK relations into a new direction, the three most important factors are mistrust between two allies (historical), diverging interests (strategic), and growing Sino–ROK ties (economic and political).