Dembele, 18, has agreed a contract at the Westfalenstadion until 2021 and is reported to have cost around €15 million.
http://www.espnfc.com/story/2870095/ousmane-dembele-joins-borussia-dortmund-from-rennes
I don't think his former club would have sold him for 15m if there was much bigger offer on the table !
The kid turned down loads of offers. Just because someone moves, doesn't mean they were available to us.