The midfielder was sold by PSV to the Premier League new boys this week.
"He lived with me in the village and is a guy I've known for ten or fifteen years. That's a different kind of connection, but I also have other guys. We're no longer carpooling anyway."
Asked if Propper can make it at Brighton, he added: "Of course, it's always possible for Dave to do well. He's on his way and he's up to that challenge. Sorry he's not here anymore.
"I wish him all the best and we're sure to be in contact."