Only needing a point from Friday night's crunch match against Croatia, Belgium won 2-1 in Zagreb to guarantee top spot in European qualifying Group A.
Jan started at left-back and played the full 90 minutes while Nacer entered the action off the bench for Romelu Lukaku on 68 minutes. Mousa then replaced Steven Defour for the final six minutes. Lukaku scored both of Belgium's goals.
Our Belgian trio have told us about the dream of travelling to the finals and now that dream is reality.
The win extended Belgium's outstanding record in qualifying to eight wins and a draw in nine matches.
They top Group A by eight points from Croatia and will complete their qualifying campaign at home to Wales on Tuesday.
It's the first time Belgium have qualified for the World Cup Finals since 2002.