Here Jan, working his way back to fitness after an ankle injury, tells us how that friendship blossomed...
Where did your friendship with Mousa start?
Jan: "I first met him when I was 12. I went to Antwerp to play for a team (Germinal Beerschot) and he played for the same team. I played for that team until I was 16. We weren’t really friends then, we knew each other and you know, he’s a good guy.
"I then saw him again in Amsterdam. When I was 16 I moved to Amsterdam to play for Ajax and when he was 18 or 19, he came to Amsterdam to play for AZ Alkmaar, which is close to Amsterdam. He lived 100 yards away from me, I knew him, I stopped by his house and that’s how it all started, in Amsterdam.
"We met again in the national team a year later when I was 20, he was already playing for the national team and that’s where we really bonded. Then he came here! He came here a couple of weeks later than me and we got close. Our girlfriends are both from Amsterdam. He became a father, I became a father and all these things helped us to get closer and closer and he feels like a friend for life."
Below: The pair stride out at the Lane
What do you remember about Mousa joining us in August, 2012?
Jan: "It was funny. I signed quite early in the window (Jan joined us in July, 2012) and his transfer was dragging on and on. I remember on the 29th of August, I called him and said ‘what’s going on? You only have two days left!’ and he said ‘yes, but I’m signing tomorrow!’ and I was very happy to hear that because I knew what kind of player Mousa is. On and off the pitch, I was a very happy guy."
Just how good is Mousa?
Jan: "I don’t think people know how good Mousa is. You can ask every single player in the team and I don’t think you can describe how good Mousa is. You can only know if you play with him or against him, see him train for a couple of weeks, then you’ll find out.
"He’s a special player and I can’t think of anyone else who is a bit like him. For me, he’s up there with the best two or three midfielders in the league. He’s a very humble guy, that’s one of his main characteristics. He’s a very special player and I certainly prefer to play with him than against him."