Karim Benzema had the ball in the net just before half time in the Champions League final but his goal did not stand.
The Frenchman had latched onto a long through pass, before jinking past Andy Robertson.
Benzema then tried to pull the ball back to a teammate but his attempted pass was weak.
Liverpool failed the clear though and a mix-up between goalkeeper Alisson Becker and center-back Ibrahima Konate saw the ball run loose.
Federico Valverde tried to intercept but Konate and Fabinho both slid in to take the ball away from him.
Fabinho deflected the ball onto Konate and then Fabinho played it again but it rolled into the path of Benzema.
Benzema proceeded to put the ball into the net, but the flag was then raised for offside.
But had Benzema been offside? That question took minutes to answer.
For starters, it was not immediately clear whether Valverde had touched the ball. If he hadn't then Benzema could not have been offside. But he had.
The next question was the one which was crucial, according to former Premier League referee Peter Walton.
Asked why Benzema had been ruled offside after the ball was played by a Liverpool player, Walton confidently told BT Sport's baffled lineup of former footballers: "It's actually quite easy to be honest with you.
"Benzema is in an offside position.
"The offense is committed if the ball is played back to him. When we see the action there, Fabinho... it deflects off him. He doesn't deliberately play the ball.
"So, because he hasn't deliberately played the ball back to Benzema, Benzema is not deemed to be onside.
"You can see that the ball defects off Fabinho. It's come off the Liverpool player but it's only played onside if the Liverpool player is deemed to have deliberately played the ball.
"That's why it took so long from the VAR angle. They were deciding whether or not Fabinho had deliberately played it."
Thanks for clearing that up, Peter...
Benzema's disallowed goal did not prove decisive as Real went on to win 1-0 thanks to a 59th-minute strike by Vinicius Junior.