The 18-year-old Japanese international, who operates largely as an attacking midfielder but can play on the wings or up front, joined Los Blancos Castilla side this summer on a free transfer from FC Tokyo.
In an official statement, the club revealed: "RCD Mallorca and Real Madrid CF have reached an agreement for the transfer of Takefusa Kubo (Kawasaki, Kanagawa, Japan, 1998) until June 30, 2020.
"The new Mallorcan player is one of the most promising players in world football and stands out for his daring nature and great quality with the ball at his feet. Kubo suits the Spanish game perfectly after passing through the academy of FC Barcelona and at 18 he is already a bonafide international with Japan.
"Kubo will train with his new teammates tomorrow at 9:30 in Son Moix."
Real Madrid also offered up a comunicado oficial on the matter, blithely declaring: "Real Madrid C. F. and R. C. D. Mallorca have agreed to the transfer of Takefusa Kubo for this season, until June 30, 2020."
Unsurprisingly, given his age and diminutive stature, Kubo has been dubbed the Japanese Messi by some. He is the youngest player to make his debut in the J-League, doing so at 15 years, five months and one day, and became the youngest ever goalscorer just five months later.
He earned his international debut at the age of 18 in July this year, during a friendly with El Salvador, and went on to play in every one of Japans group stage clashes in the summers Copa America.