The Egyptian centre-back – who was the Baggies’ highest earner on £70,000 a week – completed the move shortly before the Saudi Arabian transfer window closed at 9pm last night.
Hegazi has initially joined the Middle Eastern side on loan.
But a deal has already been agreed to make the move permanent at the end of the season. The fee for that move is officially undisclosed.
But it is understood that figure – together with the money Albion will save on Hegazi’s wages – makes the deal worth in the region of £10million to the Baggies.
Snapped up from Egyptian side Al Ahly in 2017, Hegazi has played more than 100 games for Albion.
But while he is highly thought of by head coach Slaven Bilic, he has started just 15 league games under the Croatian.
With Branislav Ivanovic, Kyle Bartley, Semi Ajayi, Dara O’Shea and Cedric Kipre also vying for a place at the heart of the defence, Albion felt the offer from Al-Ittihad was too good to turn down.
It is also believed Hegazi was keen to make the switch – with the defender set to see his wages increase from the £70,000 a week he already earns.
The Express & Star understands Hegazi was Albion’s highest earner by quite some distance.
His wages dropped to £35,000 a week while the club was in the Championship.
But they have shot up again following the club’s promotion to the Premier League. Hegazi has had interest from clubs in the Middle East ever since he arrived at The Hawthorns.
Last week reports emerged saying he was closing in on a lucrative move to Saudi Arabia.
They arrived just days after he impressed for the Baggies in the goalless draw with Burnley.
And Bilic was asked about his potential departure at a press conference called on Thursday ahead of this evening’s clash at Brighton.
Speaking then, the head coach insisted Hegazi would not be sold.
“There has been an interest in Ahmed from Saudi since I came to the club last season,” Bilic said.
“He’s a good player, and he’s from Egypt which makes him a bit more interesting for the clubs from Saudi.
“But like last year, he wants to stay here. He’s a good player, he’s playing and I’m glad he’s staying.
“I didn’t want him to go last year. This season I like him, he’s a top professional.”
But it is understood Al-Ittihad intensified their interest in Hegazi over the last 48 hours – hence why he has moved on.