According to AS, via CalcioMercato (h/t to InsideSpanishFootball's Tom Conn), the two teams agreed on a transfer fee after Inter's initial loan offer was rejected. Remarkably, the player was quoted by AS (h/t to Football-Espana) just a few days ago, saying he wanted to fight for his spot in Madrid:
"I’ll return to Madrid on July 10 to try to earn a starting spot. I’ve learned from the greats."
Madrid clearly disagrees, electing to move him to the Italian Serie A on a permanent basis, although the club holds the right to buy him back in the future should his time with Inter lead to the kind of development Los Blancos hope he can make.
Casemiro is a special talent, boasting all of the physical tools to be an elite holding midfielder. He has shown flashes of dominance in the past, and strong performances in the Brazilian youth teams led to Real making a move for his services.
For all of his physical tools, however, the mental side of the game poses a problem for the Brazilian. Bleacher Report's Sam Tighe wrote an extensive scouting report on the player a year ago, when he joined Real, and much of what he found still holds true today.
Casemiro has an attitude problem, as detailed by Brazilian football expert Chris Atkins, via Tighe:
Casemiro went to U20 World Cup (where he did reasonably well), but lost form on his return. Lucas Moura also suffered, and Sao Paulo's season quickly fell apart.
Denilson's arrival on loan from Arsenal and the changing of several managers saw Casemiro dropped to the bench, and his attitude started to become a problem. He was criticised by coaches for not working hard enough, and he often looked overweight.
He never recovered; Sao Paulo went on to win trophies with Wellington and Denilson controlling the midfield. Even in Wellington's long absence with a knee injury early in 2012, Casemiro was often overlooked as a starter.
It all came down to the same criticisms: lack of work ethic and poor fitness levels.
Now, Real Madrid are too great a club to invest too much time in a young player unwilling to work for his spot amongst the very best. A sale makes perfect sense from that perspective, and given the player's potential, the buy-back clause make this deal a no-brainer.
The problem with this transfer move is the team the player is headed—Internazionale. The Nerazzurri finished fifth in Serie A last season, and manager Walter Mazzarri is under real pressure to perform in 2014-15.
More was expected from the former Napoli man last season, and the coming campaign will be a make-or-break year for Mazzarri, who doesn't have the greatest track record when it comes to developing youngsters.
The same can be said for the entire club—the Primavera won the 2012 edition of the NextGen series, but none of the players from that squad were ever given a real chance to make their mark for the team's senior side.
Mazzarri isn't about to gamble his future in Milan on a 22-year-old prospect in need of guidance. Casemiro might get a chance to play immediately, but the club isn't going to make his development a priority.
One club who would have done so are city rivals AC Milan, whose new manager Pippo Inzaghi was reportedly keen on bringing Casemiro to the Italian capital of fashion earlier this month, per Sportmediaset (h/t to Football-Italia).
Inzaghi is a former Milan Primavera coach who has built a reputation for being a magician when it comes to working with younger players, and unlike Mazzarri, he will be given time to grow into his new job with the Rossoneri.
The former Italy international handpicked Casemiro and would have relished the opportunity to work with such a talented, albeit troubled player.
Playing time would have been almost assured, and with young talent like Hachim Mastour and Bryan Cristante around him, the foundation for Milan's midfield would have been very, very solid.
The chances of him developing into the player Real know he can be would have been far greater, and the buy-back clause would have seemed so much more appealing in that scenario.
Instead, Casemiro will be entering an environment where help won't be readily available, and he'll be playing for a coach who is more interested in winning today than building for tomorrow.