While the vast majority of United fans will be sorry to see Giggs leave, few will be surprised.
The Premier League's all-time assists leader once described his time in charge of the club after Moyes' exit as the "proudest moment" of his career - a spell that brought two wins, a draw and a defeat.
And in April, Van Gaal told MUTV: "I expect that (Giggs) will be the next manager after I am gone.
"What he has to do, for me, he does it very well."
Giggs never looked entirely comfortable sitting alongside the Dutchman during last season's erratic campaign but he is reported to have been angry at the insensitive handling of Van Gaal's sacking, coming, as it did, in the immediate aftermath of United's FA Cup victory.
If that put him slightly at odds with the club's hierarchy, led by executive vice-chairman Ed Woodward, Mourinho's arrival has tipped the balance, particularly as the Portuguese himself has shown no real enthusiasm for working with a potential rival.
That said, there was still some hope at United that Giggs - arguably the last link to Sir Alex Ferguson's great sides still closely involved at the club - could be tempted with a role that bridged the academy and the first-team set-up.
However that was dressed up, though, it was still a demotion and Giggs is no doubt also well aware of Mourinho's preference for more experienced, bought-in solutions than placing his trust in home-grown youngsters.
Mourinho, who was sacked by Chelsea in December, reports to United's training ground at Carrington for the first time on Monday.
Giggs, on the other hand, will be looking for another place to prepare for the new season for the first time since arriving at United as a 14-year-old in 1987.