The attacker has signed a four-year deal with the Nerazzurri and will join his new club at the end of the season.
The 18-year-old travelled to Milan on Monday to undergo a medical and to finalise negotiations, and Feyenoord have now confirmed the transfer on their official website.
“My visit to Inter was a great experience. I immediately noticed in Milan how everything in Italy is about football. They gave me a warm welcome before I underwent a thorough medical exam. I then signed the contract at the Inter headquarters, “said Castaignos to the Dutch club’s official website.
“I’m very pleased and proud that I’ll be a player of one of the best teams in the world next season. I haven’t met the coach yet, but there’s plenty of time for that this summer.”
Castaignos is a product of the Feyenoord youth academy and has so far scored nine goals in 28 Eredivisie appearances for the beleaguered Rotterdam side.
Inter Sign Luc Castaignos From Feyenoord