Summary:
Manchester United and Chelsea are close friends, according to the pair's biography.

Full article:
Chelsea manager Jose Mourinho has revealed he used to go home and moan about working under Louis van Gaal to his wife during his time under the Dutchman at Barcelona. Van Gaal chose to keep Mourinho on his coaching staff after taking over the reins at the Nou Camp from Sir Bobby Robson in 1997. The two Premier League bosses have revealed in the run up to Sunday's match between Manchester United and Chelsea that they remain good friends, however the pair's relationship has not always been rosy. VIDEOS Scroll down to watch . Louis Van Gaal decided to keep Jose Mourinho at Barcelona after taking over reins at the Nou Camp . Mourinho, pictured with Van Gaal in 2010, grew frustrated at working under the Dutchman . Mourinho said in his official biography: 'Every day I would go home and moan to my wife that Van Gaal does it this way, but I would do it that way. 'The break between us happened out of necessity and not out of choice. Why would I want to leave there? I would leave one day as a consequence of something. That's what happened, when Van Gaal took over as Dutch national coach. From there I took my own path. 'Van Gaal met me and said he wanted me by his side because of the influence I had in the previous coaching team.' Portuguese tactician Mourinho felt he had to leave Van Gaal's coaching team in order to progress . Quotes taken from Luis Lourenco's Jose Mourinho: Made in Portugal .