A fan was ejected from a U.S. Open tennis match early Tuesday morning after German player Alexander Zverev complained the man used language from Adolf Hitler’s Nazi regime.

Zverev, the No. 12 seed, was serving at 2-2 in the fourth set of his match against No. 6 Jannik Sinner when he suddenly went to chair umpire James Keothavong and pointed toward the fan, who was sitting in a section behind the umpire.

“He just said the most famous Hitler phrase there is in this world,” Zverev told Keothavong. “It’s not acceptable.”

“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,” Zverev said.