As tensions flare on the Korean peninsula, China's management of this partnership will have a dramatic impact on the stability of Asia and beyond.
North Korea's friends need to call for calm
Some relationships, to quote Winston Churchill, are "special". Think America and Britain post-Second World War, and Israel and the United States today.
Less obvious, but arguably more unique, are the ties that bind China and North Korea. As tensions flare on the Korean peninsula, China's management of this partnership will have a dramatic impact on the stability of Asia and beyond.
Events in recent weeks underscore the need for close friends to talk sense in a volatile region. In late November, four South Koreans were killed in a barrage of missiles launched by the north, and Seoul is now planning a series of artillery tests as a show of defiance.
All of this shouting demands a vocal retort. Yet China, with more influence than anyone else over North Korea, has largely recycled vague talking points and renewed calls for talks that the north has frequently mocked.
This response isn't new - China notably failed to condemn the north's attack on a South Korean warship in March, which killed 46 South Korea sailors. But it isn't helpful, either. What North Korea needs to hear from Beijing is a strong reprimand, not silence that can be taken as consent. There will be a time for negotiations, but returning to them now would reward North Korea for behaving badly, which benefits no one but Kim Jong-il.
Just how much leverage China actually has over its eastern neighbour is debatable. Pyongyang's leadership has always been deeply distrustful of outsiders, and is likely to be wary of China's motivations.
But it is also true that Beijing has more than enough economic leverage to push North Korea to act more responsibly. China remains Pyongyang's only major supplier of food and fuel, aid that helps prop up a brazen dictatorship. Threats to cut these handouts might actually force the elusive Mr Kim to listen, or risk watching his regime crumble.
Unfortunately, instability may find the Koreans regardless of China's actions. As the mounting tensions between Pyongyang and Seoul make clear, South Korea appears no longer content to exercise restraint. South Korean President Lee Myung-bak's government has faced domestic criticism for backing down in the past. It appears less willing to do so now.
As the unofficial US envoy, Governor Bill Richardson, warned yesterday, the situation on the Korean peninsula has become a "tinderbox" of tension. The US should use its influence to remind South Korea it can't afford to take Mr Kim's bait. More important, though, is for the region's other "special relationship" to mature. In the end, China's cajoling of its unpredictable partner may be the only way to avert a return to all-out war.