After days of speculation, it has been confirmed that North Korea's leader Kim Jong-un did pay a visit to Beijing.
The visit, confirmed by China and North Korea, was Mr Kim's first known foreign trip since taking office in 2011.
He held "successful talks" with President Xi Jinping, China's Xinhua news agency reported.
China is North Korea's main economic ally and it was thought highly likely it would consult Beijing before planned summits with South Korea and the US.
Mr Kim is due to meet South Korean President Moon Jae-in in April, and US President Donald Trump in May.
The Beijing visit is considered a significant step in North Korea's preparation for the proposed talks.
Mr Kim arrived with his wife, Ri Sol-ju, by train on Sunday and left Beijing on Tuesday afternoon, according to reports.
During the visit, Mr Kim assured his Chinese counterpart he was committed to giving up his nuclear weapons, Xinhua reported, but with conditions.
"The issue of denuclearisation of the Korean Peninsula can be resolved, if South Korea and the United States respond to our efforts with goodwill, create an atmosphere of peace and stability while taking progressive and synchronous measures for the realisation of peace," Mr Kim was reported saying.
The North's conditions include the removal of a US nuclear guarantee for South Korea, observers say.
North Korea's KCNA news agency called the visit "a milestone" in improving bilateral ties.
Mr Kim's arrival and departure were shrouded in secrecy. China said the visit was "unofficial" - so there was no announcement of it in advance, prompting speculation about who was on the train when it was spotted arriving.
Because of the unofficial status of the visit, some of the normal protocols for foreign visits were not observed. For example no North Korean country flags were hung around the Great Hall of the People on Tiananmen Square.