After years of speculation, Jose Mourinho has confirmed that he agreed to replace Sir Alex Ferguson at Manchester United in 2013, before changing his mind and re-joining Chelsea instead.

"When I left Real Madrid, I signed to go to Manchester United after Sir Alex," the 63-year-old coach - now back at Real for a second spell - said in a new Netflix documentary series about his career.

"He was offered the job, yes," confirmed Ferguson, who won 13 Premier League titles over 26 years at Old Trafford before retiring in 2013.

"I sat him down and explained the situation," he added: "As far as I was concerned, he was accepting. And then, within hours, it changed."

What changed was that Mourinho felt he could not turn down a return to Chelsea, where he had won consecutive Premier League titles in 2005 and 2006.

"One night, he phoned me and he was crying and he says, 'Alex, I can't take it. I've given my word to Chelsea and I'm not going to break my word'," said the former United boss.

"The reason he gave to me, I could understand, but I was disappointed."

Mourinho said he was "very flattered" to be offered the job of replacing Ferguson "because Manchester United has an incredible appeal".

"But one thing is love for football, another thing is love for a certain club," he explained.

"I think this is more powerful than love for football and fundamentally, after Real Madrid, I needed to feel that I'm loved.

"For me to lose the chance to be the coach to succeed Sir Alex Ferguson was dramatic, but I don't regret it because it was a decision that I made with my heart."

After returning to Stamford Bridge in 2013, Mourinho went on to win his third Premier League title and the League Cup.

In May 2016, he got a second chance to take over at United, succeeding Louis van Gaal.

Over a two-and-a-half-year spell at Old Trafford, Mourinho won the League Cup and Europa League titles before being sacked in December 2018 following a slump in results.

He returned to another of his old clubs, Real Madrid, in May this year. Mourinho's last spell there ended in acrimony as he fell out with club captain Iker Casillas and other players.

On the eve of his Real reunion, the combative manager and former Spain goalkeeper Casillas spoke candidly about the reasons behind those differences.

Mourinho also spoke about difficulties he has faced with former Chelsea owner Roman Abramovich, who hired him twice and sacked him both times.

'The relationship I had with Jose was very cold'

After taking over a struggling Real side, Mourinho helped them challenge the dominance of Pep Guardiola's Barcelona, winning La Liga, Copa del Rey and Spanish Super Cup trophies in his first two seasons at the Bernabeu. The 100 points they amassed in 2011-12 remains a La Liga record.

However, the wheels came off in Mourinho's third season in the Spanish capital and he was dismissed at the end of 2012-13 with Real finishing 15 points behind rivals Barcelona.

His treatment of Casillas divided the dressing room. The goalkeeper made 725 appearances across 25 years at Real, winning three Champions League titles and five La Liga crowns, but had spent much of the 2012-13 season on the bench.

"The relationship Jose and I had was very cold," he said.

"In those years, I really think it was taken to a limit where in the end, the rope broke."

Former Real midfielder Sami Khedira said that Mourinho's rift with Casillas affected everyone.

"Iker is a Real Madrid legend, loved by every Real Madrid supporter. He benched him, doesn't speak to him, spoke bad about him in the media, so then this locker room was a nightmare, honestly," he said.

"After that, the relationship between Jose and many, many players was broken – like Cristiano [Ronaldo] and the Spanish guys, Casillas, Sergio Ramos. And those players were super, super important for the atmosphere in the locker room."

Mourinho claimed that the keeper had a bad attitude.

"The first three times that I spoke to Casillas, the captain, the first thing he told me was, 'I want to ask for more holidays for the national team players'," he said.

"The second time he spoke to me was, 'I would like to ask you to put the training sessions one hour later because at the time you want the training sessions, there is a lot of traffic in Madrid'. The third time he comes to speak with me was, 'We don't want to go to [the] hotel. We prefer just to meet on matchday and go direct to the stadium to play'. And in a short period of time, I realised they're spoilt."

Former Spain captain Casillas also revealed that he clashed with Mourinho over the manager's attitude towards his international team-mates who played for Barcelona.

The 63-year-old's response was unapologetic.

"There are things that I don't accept and I will never accept and when somebody doesn't respect me, it's a problem. I say, this is Barcelona, Real Madrid. When you go to the national team, then you can kiss the guy, but not now. This is war."

'I was playing against Roman that game' – on Chelsea sacking

Mourinho was sacked by Abramovich at Chelsea in 2007 and 2015.

The veteran manager said that his former boss became increasingly interfering during his first spell at the club, including pushing for the signing of Andriy Shevchenko.

The Ukraine striker joined Chelsea in May 2006 for a then club record fee of approximately £30m, but scored only nine league goals in 48 games over a three-year spell in West London.

"Abramovich - incredible passion for football, but knowing nothing about the situation," Mourinho said.

"Shevchenko was on the table because of connections with the boss, connections with agents and I never wanted to sign him, but I never told no one, so it's also my responsibility. You want to know the player that I wanted? [Samuel] Eto'o."

Following his dismissal by the Russian oligarch in September 2007, Mourinho had a chance for revenge when he returned to Stamford Bridge in February 2010 with Inter Milan in the last 16 of the Champions League. The Italian side beat Chelsea 2-1, before going on to win the title.

"Honestly, I was playing against Roman that game," Mourinho said.

"I was playing against a guy that sacked me. I go home happy and he goes home upset. Because I know how much he loved Chelsea, I know how much he loves to win.

"But I needed revenge, because football belongs to people like me. The other ones are the intruders that don't belong. Football belongs to the players, belongs to the coaches, belongs to the fans. Football will always belong to us."