The Bees have splashed the cash to bring in the Dutch centre half late in the transfer window.
The 22-year-old has moved for a fee of £25 million and has already put pen to paper on a long term contract.
“I've been waiting for this moment for a long time now. I had a few phone calls and a meeting with the manager, where he told me why they wanted me here, they showed me what qualities they see in me as a player, so it was all positive,” he said about signing for the Bees and their boss Thomas Frank.
"I just want to help the team wherever I can. Personally, playing as many games as I can, that's what I came here for. I also want to develop myself and help the team achieve things that have never happened before - maybe Europe - you have to dream big!
“I want to just enjoy being here, that's the thing for me. I also want to bring passion, defending, and just giving everything I have, leaving it all on the pitch. And I want to play a lot of games in front of the fans, and hopefully I can see them a lot in the stadiums, home and away.”