The 21-year-old midfielder, who is a product of the Chelsea academy, signed a three-year deal with the Championship side after his contract with the Blues expired earlier this summer.
The England U21 international also turned down interest from Brentford, where he spent last season on loan.
"I met him and that made up my mind… he's someone to learn from, someone who has been at the very top level.
"Obviously he didn't play in the same position as me but I can definitely learn from him every day in training.
"But I was playing on the left there last season. Obviously I enjoyed it but I didn't want to just settle on that. I wanted to look everywhere else.
"So luckily I waited, then Jaap came in at Reading and it was all done and dusted."