North Korean leader Kim Jong Un’s trip to Vietnam for a summit with U.S. President Donald Trump was shrouded in mystery until a green train with yellow horizontal stripes was spotted crossing the Yalu river into China on Saturday evening. Kim, his father and grandfather, North Korea’s three leaders in succession since World War Two, have all loved trains, but no one knew how Kim intended to make the journey to Hanoi for his second summit with Trump, on Wednesday and Thursday, until the train rumbled over the border bridge.