Reuters
Early on Monday morning, heavy security descended on the Friendship Bridge, the border crossing over the Yalu River that separates North Korea from China.
A green and yellow train then crossed the bridge, transited several stations, and arrived at the Beijing Railway Station.
The station had an unusually large security detail, as did the Diaoyutai State Guesthouse, where foreign dignitaries stay during state visits to China.
All of this led analysts and onlookers to come to a likely conclusion - someone important from North Korea was visiting China. Rumors swirled it could be Kim Jong Un, or his sister, Kim Yo Jong.
It would not be the first time. Kim's father and grandfather both visited China, the North Korea's most important ally and the source of much of its trade and goods. Kim plans to meet South Korean President Moon Jae-in in late April, as well as with US President Donald Trump by May, meaning this trip could be a precursor.
Here is everything we know about the mysterious train and the secret guest's convoy: