A fan attending Monday night's U.S. Open match between Germany's Alexander Zverev and Italy's Jannik Sinner was ejected after shouting "the most famous Hitler phrase" from the stands.

During the fourth set of the match, Zverev approached the chair umpire and complained, pointing in the direction of the fan:

“He just said the most famous Hitler phrase there is in this world."

“It’s not acceptable.”

Despite the request of the chair umpire James Keothavong, the fan did not identify himself.

Just after the set, however, the fan was identified by nearby spectators and was removed by security.

People on social media applauded Zverev for calling attention to the unacceptable behavior.

Zverev later explained in an interview exactly what the fan was yelling.

“He started singing the anthem of Hitler that was back in the day. It was ‘Deutschland über alles’ and it was a bit too much."

He continued:

“I think he was getting involved in the match for a long time, though. I don’t mind it, I love when fans are loud, I love when fans are emotional."

"But I think me being German and not really proud of that history, it’s not really a great thing to do and I think him sitting in one of the front rows, I think a lot of people heard it. So if I just don’t react, I think it’s bad from my side.”

Zverev himself summed it up perfectly:

“It’s his loss, to be honest, to not witness the final two sets of that match."

Zverev ultimately took the win over Sinner in five sets in the match that lasted a grueling 4 hours and 41 minutes—the second-longest U.S. Open match ever.