The Serbia international was desperate to leave London after a Saudi bid was submitted earlier this summer.
So much so, that he told coach Marco Silva that he did not want to play for the club over pre-season for Fulham.
And the striker has got his wish, flying to the Middle East after passing a medical in France.
He will partner Neymar, who made a high-profile switch from Paris Saint-Germain on Tuesday, as well as former Zenit St Petersburg and Barcelona star Malcom.
Al Hilal have also signed Ruben Neves from Wolves, Sergej Milinkovic-Savic from Lazio and Kalidou Koulibaly from Chelsea this summer.
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It is part of an aggressive policy from the Saudi Pro League to snap up the best and biggest players possible.
As well as Al Hilal, Al Nassr, Al Ittihad and Al Ahli have all received government backing to spend seemingly at leisure to bring in whoever they want.
Mitrovic's arrival is just one of several players to have moved to the Gulf State, including Karim Benzema, Riyad Mahrez and N'Golo Kante.
The forward had returned to first-team training ahead of the Premier League season and made an appearance against Everton, aiding in Fulham's winner.
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That is despite vowing to never play for the club again, though the reunion was always short-lived as Silva admitted that the situation was not easy.
Silva said earlier in the summer: "Yes, Mitrovic is back. It is a process and it is not an easy situation.
"I am not here to talk about the negotiations and clubs that are linked with him. I am here to talk about my players.
"Yes, he is with the group. Let's hope we get him as fit as we can in the next few days.
"For me, Mitrovic never was hard to manage. Never, never, never.
"A lot of people say he has an aura around him but people who know him know he was never a problem or difficult to manage.
"We have to be honest with him. He was so easy to manage in the beginning of the pre-season and he will be if he stays.
"Mitro knows me, I know him very well. He knows the group we are working with.
"Everything I said to him and everything he said to me will be between me and him."