There is an option to buy from Paris St-Germain for the Dutch player.
The captain of the Netherlands won the title and made 37 appearances after moving to Paris.
He can be bought by the Italian club after the22-23 season.
Jose Mourinho has signed five summer signings.
He's following in the footsteps of other people to the Italian capital.
It's a good feeling to be a player for the Giallorossi. Everyone I've spoken to has positive things to say about the club.
The club made it clear to me how much they wanted me to do in order to complete the deal, which gave me a lot of confidence and belief. The reception from the supporters has been great.
I will help the team compete for all their goals this season.
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