Middlesbrough manager Aitor Karanka says Manchester United boss Jose Mourinho is a different man away from the pressure of football.
Having previously worked as Mourinho's assistant at Real Madrid for three years, Karanka will take on his old mentor for the first time on Saturday when Boro visit United.
Mourinho's mind games off the pitch and his antics on the sidelines are well documented, but the Boro boss insists there is more to the Portuguese than meets the eye.
Asked if he is different away from football, Karanka said: "A little bit. Yes, he's different.
"He's different because it is impossible to live 24 hours with that pressure, with that tension that he puts into every single training session or every single game.
"He is different. We are really good friends and we have a really good relationship. But it's football, it's 90 minutes, so for 90 minutes, you can't be friends.
"At the end of the game, we will have a glass of wine, a beer or a Coke and one of us will be happier than the other.''
A little more than three years into his first managerial post, Karanka acknowledges that he would not be where he is but for Mourinho -- who has said his former assistant has improved as a coach.
Asked what makes the United manager tick, Karanka replied: "It's a mix of everything: his knowledge, his character, his passion, his personality -- he has a lot of things.
"The way that he prepares the game is the best; the way that he trains is the best; the way that he is in the changing room is the best, so it's a lot of things and for that reason, he is the best.
"The best example is the relationship he has with the players when he leaves clubs. He has a really good relationship with them all.
"For sure, the players always want to play, but he has a very good relationship with most of the players who have been with him because if he goes to Arsenal, you can see him with [Mesut] Ozil giving him a hug, or when he goes to other places, he has a very good relationship.''
Karanka says he has learned from Mourinho the necessity to be brutally honest with players when the need arises.
The Spaniard said: "I have said a lot of times that to be honest is the best thing. For me, my biggest concern was to do with the players the things that some managers had done with me.
"I had three years with Jose and looking at him treating the players in that way, now I am treating the players in that way, and telling them sometimes things they don't want to hear is the best way.''
Karanka has already guided his promoted team to creditable draws at Arsenal and Manchester City, and is working on a plan which may include a surprise for his opposite number.
He said: "I'll try -- but it's difficult to surprise Jose.''