Manchester City boss Pep Guardiola has developed an infamous rivalry with former Manchester United manager Jose Mourinho over the years.
The duo were known to be friends at Barcelona, where Guardiola was a player and Mourinho worked as Bobby Robson's translator, but the relationship has soured since the pair became managers.
We've taken a look at their war of words over the years.
April 2010
One of the first meetings between the two managers came in the Champions League semi-finals of 2010 when Mourinho's Inter faced Guardiola's Barcelona.
After Inter recorded a 3-1 victory at the San Siro in the first leg, Mourinho said: “A year ago Chelsea were crying and Barca were laughing with the referee” – referring to the previous season's Champions League semi-final at Stamford Bridge in which referee Tom Henning Ovrebo made a number of controversial decisions.
“They laughed because he denied my Chelsea boys their rightful place.”
Barcelona won the second leg 1-0, but it was not enough to overturn the deficit as Inter went on to beat Bayern in the final.
“It is the most beautiful defeat of my life,” Mourinho said after the loss in the Nou Camp. “It is a style of blood not skill.
“We were a team of heroes. It's a pity I could not play because I have got the same blood. I have already won a Champions League but today was even better. We made huge sacrifices.”
April 2011
With Mourinho then installed as Real Madrid manager, the two sides face off in a period of four Clasicos in 18 days,
After Real triumph 1-0 in the Copa Del Rey final, Guardiola rues the (correct) decision to disallow a Pedro goal: “A two-centimetre decision from a linesman who must have had a very good view ruled out Pedro's goal.”
Mourinho responds with a jibe at Guardiola for criticising referees even when they make correct decisions. Jose's dig prompts an irate response from the Barca boss in his press conference prior to the two sides' meeting in the Champions League semi-final.
“In this room, Mourinho is the f*cking chief, the f*cking boss. I don't want to compete with him in here… but this is a game of football.”
Barca go on to win the first leg of the semi-final 2-0, with Pepe receiving his marching orders and Mourinho also sent to the stands. The Real manager promptly embarks on a stunning rant.
“One day, I would like Josep Guardiola to win this competition properly. If I tell UEFA what I really think and feel, my career would end now.
“Instead I will just ask a question to which I hope one day to get a response: Why? Why Ovrebo? Why Busacca? Why De Bleeckere? Why Stark? Why? Because every semi-final the same things happen. We are talking about an absolutely fantastic football team, so why do they need that? Why?
“Why does a team as good as they are need something [extra] that is so obvious that everyone sees it? I don't know if it is the UNICEF sponsorship or if it is because they are nice guys.
“I don't understand. They have power and we have no chance. All I can do is leave that question here in the air and hope that one day I will get the response.
“They have to get to the final, and they'll get there, full stop. Josep Guardiola is a fantastic coach. But I have won two Champions Leagues and he has won only one Champions League – and that is one that would embarrass me.
“I would be ashamed to have won it with the scandal of Stamford Bridge. If he wins it this year, it will be with the scandal of the Bernabeu. Deep down, if they are good people, it cannot taste right for them. I hope one day Guardiola has the chance of winning a brilliant, clean championship with no scandal.”
April 2012
Guardiola announces he will leave Barcelona at the end of the season, with many reports suggesting his rivalry with Mourinho has intensified the burnout he suffered in the job. Mourinho, however, has little sympathy.
“It's his life, but for me it's unthinkable to take a sabbatical,” he said. “He is younger than me but I'm not tired.”
August 2013
A year after leaving Barcelona, Guardiola takes over at Bayern Munich and Mourinho returns to Chelsea for a second spell.
As fate would have it, the duo are pitted against each other again in the UEFA Super Cup, with Bayern triumphing in a penalty shootout after Ramires was sent off towards the end of normal time.
“Every time I play Pep I end up with 10 men,” Mourinho said. “It must be some sort of UEFA rule.”
He added: “The best team clearly lost. They just scored one more penalty.”
September 2014
At a UEFA Elite Club Coaches Forum, the duo argued about – wait for it – the ideal length of grass, with Guardiola preferring a surface no longer than 1.5cm in order to speed up play.
“Everyone has his style of play, which should be respected,” Mourinho said, according to TZ. “Football can be spectacular in several ways.”
Guardiola responded: “The beauty of football depends on the coach. It seems to me that Mourinho prefers the result to the spectacle. I know to him that's all that matters.”
According to El Confidencial, Mourinho later said: “When you enjoy what you do, you don't lose your hair, and Guardiola is bald. He doesn't enjoy football.”
May 2015
After securing the Premier League title in his second spell at Chelsea, Mourinho appeared to take a swipe at Guardiola, who had just won a second-consecutive Bundesliga with Bayern Munich.
“For me, I'm not the smartest guy to choose countries and clubs. I could choose another club in another country where to be champion is easier.
“I choose a club where I was happier before and a country where you are happy before. I took a risk. I am so, so happy because I won another Premier League title 10 years after [my first] in my second spell at the club.
“I was champion at every club I coached. I came to Inter, Real Madrid and Chelsea. Every title is important, to win the title in Spain with 100 points against the best Barcelona ever was a big achievement that I enjoyed so much.
He added: “Maybe in the future I have to be smarter and choose another club in another country where everybody is champion. Maybe I will go to a country where a kitman can be coach and win the title.”
September 2016
Guardiola's appointment at Manchester City was hugely anticipated thanks in no small part to the fact it coincided with Manchester United's hiring of Mourinho.
However, ahead of the first derby clash between the two, Mourinho admitted neither manager could afford to get caught up in the rivalry.
“In a situation like this (Spain), individual fights make sense because they can influence things. (But) in the Premier League, if I focus on him and Manchester City, and he on me and Manchester United, someone else is going to win the league.”
August 2018
City's title-winning season under Guardiola featured a bust-up between the two sides in the tunnel at Old Trafford, with United unhappy at the visitors celebrating a 2-1 victory by blaring music out of the changing room.
In City's behind-the-scenes documentary on the campaign, one episode features the December derby victory, with narration saying: “Guardiola versus Mourinho once more; possession versus defence; attacking football versus 'park-the-bus.'”
Mourinho is left unimpressed.
“You don't need to be disrespectful to have a fantastic movie. You can be a rich club and buy the best players in the world but you cannot buy class and they showed that clearly, that was really obvious,” he told Sky Sports.
Guardiola later replied: “That is true, you cannot buy class. I agree with Jose. We cannot buy class. I think we lived an amazing season with cameras. We did it for ourselves. I don't agree with Jose in terms of disrespectful. This was not our intention – it was to film last season.”