Found it mate, it’s this episode from the 22nd minute.
Mitten has amazing connections within United and in Spain (where he lives). If he goes on record to say something, you can guarantee someone well connected has said it to him. Whether it’s true or not is a different story, but he always comes through with what he hears from people who are making the decisions at big clubs.
Also, the fax machine story is more fun than the actual answer, which is Madrid started stalling because they wasn’t sure about the deal.
It really was a strange situation.
Throughout the entire 2015 transfer window it was very obvious that Real wanted De Gea to kick up a fuss and force us to sell him for a low fee. While he made it obvious he did want us to sell, I'll give him credit that he didn't do anything to really cause problems and simply sat back expecting Real to eventually pay the fee it would take. Finally right at the end of the window it seemed that they agreed to do so, but then of course it fell apart as the window closed. Then a couple of weeks later De Gea signed a new contract.
In the 2016 transfer window Real once again showed interest to see if De Gea would kick up a stink, and this time he showed no interest at all and they quickly moved on and were never linked again.
Real certainly didn't 'want' to spend what we were demanding which is why it ended up going down right to the last minute, but just what caused the final failure is something we'll probably never know. Did they deliberately let time run out because they thought they could get him for that cheaper price 12 months later? Did we deliberately let time run out because we didn't actually want to sell him? Or did both clubs truly agree but it was so late that communication and technical issues wrecked the deal? Any of the three wouldn't surprise me. Whichever it was, De Gea certainly didn't seem too impressed with Madrid's messing around with the deal seeing as he quickly signed his new contract with us and didn't return the interest they showed the following season.