The Brazilian fullback is set to move to Lyon in the near future after seven years at Old Trafford.
The two players were main men in the Red Devils' most Premier League triumph in 2012-13, the season after the Spaniard moved to Old Trafford, which was also Sir Alex Ferguson's final campaign in charge of the club.
Rafael played 40 matches that year as the club's first-choice right-back, while De Gea dispelled doubts regarding his ability and underlined his quality as one for he best young goalkeepers in the world. Understandably, there is a bond between the two, as evidenced by the former Atletico Madrid man's message to the defender.
That title winning season was however Rafael's only campaign of 20 or more Premier League matches, despite featuring for United in seven or more seasons since he and twin-brother Fabio arrived as 18-year-olds in 2008. The Brazil international struggled in David Moyes time in charge at the club, and was unable to convince Louis van Gaal of his quality, despite the absence of a genuine right-back at the club.
He will now try his hand in French football, with Lyon also set to compete in the Champions League this season.