Gilmour was one of the brightest young talents in the Rangers academy and he was regularly training with the first team when Mark Warburton was the manager at Ibrox.
He caught the eye of Chelsea’s scouts with his performances in youth football and he was snapped up by the Blues academy in 2017.
Rangers wanted to keep the youngster but he was eventually allowed to move to Chelsea for a significant compensation fee four years ago.
Mulholland revealed that it was a great deal for Rangers and the significant add-ons mean the club have financially benefited from Gilmour’s move south of the border.
He stressed that keeping hold of their best youngsters is still what Rangers want to do, but stressed that in most academies some players do leave.
The Rangers head of academy told The Athletic: “The deal we got was a significant number at the time and has some more significant add-ons after that, which are a positive for Rangers.
“It has a really good sell-on so every time he does well with Chelsea or makes his debut for Scotland, for example, there is a further return for Rangers which justifies the investment in the academy.
“It’s not part of the business model we ever want as we want to retain our best talent and get them to the first team as there is even more value there but in every academy in the world we will always have players leave as part of player trading.”
Gilmour is part of Chelsea’s first-team squad and now has a Champions League winner’s medal.