The 63-year-old has snubbed a fresh contract offer from Benfica to return to the club he managed from 2010 to 2013.
That is according to Fabrizio Romano, who revealed that Real were given Mourinho's "green light" to take over at the Bernabeu, 13 years after exiting the Spanish capital.
Mourinho "never had any doubts" over the call to join the 15-time Champions League winners, despite recording a second successive trophy-less season after losing to Barcelona on Sunday.
In fact, the Portuguese boss is apparently "super excited" about managing Los Blancos, even though the club is currently going through some turmoil.
Fede Valverde was recently sent to hospital following a fight with Aurelien Tchouameni, while several Real Madrid players are no longer on speaking terms with Alvaro Arbeloa.
Whether Mourinho is the right appointment to fix this mess remains to be seen, but he's not won a league title in over a decade, and that doesn't bode well for a team who crave constant success.