The Portuguese coach, back at the Bernabeu 13 years after his first spell ended in 2013, flew into Madrid and headed straight to the Valdebebas training complex, where he was already working alongside his coaching staff by the morning.
Mourinho has brought a trusted group with him for his second spell in charge, with Joao Tralhao as assistant coach, Antonio Dias overseeing fitness, Pedro Machado continuing as analyst, and Roberto Merella and Nuno Santos completing the technical team.
"We've been working hard. It's not that I arrive here today and everything starts," Mourinho told Real Madrid TV. "We've been working hard for a long time with the club's structure at different levels.
"Nowadays you can work without being here because technology helps us enormously, and today has basically been about arriving and 'checking' everything that has been done and everything we still have to do."
The 63-year-old described his return as something close to a calling.
"Words aren't enough because it's like a mission," he said. "It's not about being worried about myself or about whether I'll earn a lot or a little. I'm here to help everyone become better: players, staff. To create a culture of work, of responsibility, of ambition, and of something I know well, which is the responsibility and the honour of working for Real Madrid.
"I really like this concept. It's not about working at Real Madrid, it's about working for Real Madrid. And it's with this spirit of mission that I'm here."
Pre-season officially begins on Monday, when available players report for medical examinations before Mourinho takes his first formal training session that evening. Real Madrid will be without their World Cup contingent for the opening weeks, meaning only Andriy Lunin, Trent Alexander-Arnold, Raul Asencio, Alvaro Carreras, Dean Huijsen, Eduardo Camavinga, Gonzalo and Franco Mastantuono will initially be under Mourinho's charge, while Eder Militao, Ferland Mendy and Rodrygo continue their recovery from serious injuries sustained late last season.
"We have to make the most of the next two weeks with positivity, because obviously I'd like to have all the players here," Mourinho said.
"We have to look at it in a positive way, which is getting to know the boys I'm going to work with and giving them the chance to get to know me too. During pre-season a lot of these boys will be here from Castilla, and I like to get involved and help this area grow too.
"Here we are, and some World Cup winner will arrive eventually. With a lot of confidence, with a lot of feeling that I love this club, and Hala Madrid and nothing else!"
Mourinho's formal unveiling as head coach will not take place until after the World Cup, by which point he will already have overseen several sessions with his depleted early squad.