It was a visit shrouded in mystery and rife with speculation. There is no word yet as to who exactly was on the train that left North Korea for the Chinese capital and is now on their way back. But if it was Kim Jong-un, as many believe, it would be the North Korean leader's first foreign trip since he came to power in 2011.
China's foreign ministry has denied any knowledge of the visit.
Al Jazeera's Adrian Brown reports from Beijing.
