Since then, there have been no high level exchanges between the two former allies.
Indeed the last high-profile foreigner to spend quality time with the young Kim was Dennis Rodman, the eccentric former NBA basketball star.
"You have a friend for life," Rodman told Kim after the two men sat next to each other to watch a basketball exhibition in Pyongyang in March. The meeting showed another side of a young man thrust into the seat of power with much to prove, according to Korea watchers.
Christopher Hill, a former U.S. ambassador to South Korea, said the flurry of tough talk out of Pyongyang shouldn't be ignored, but it could be directed to the citizenry itself. "I think there's a big element of domestic North Korean politics, if one can understand that concept, where clearly Kim Jong Un is not being well received," Hill told CNN recently.
"I think they are trying to kind of boost his status to some sort of wartime leader."
It remains to be seen how far the relatively inexperienced leader will go to shore up his position at home -- even if this pushes the North's traditional ally too far.