President Joe Biden mistakenly introduced Ukrainian President Volodymyr Zelenskyy as “President Putin” on stage at the NATO summit at a ceremony marking the signing of a security agreement for Ukraine.

The gaffe came at the end of a speech by Biden about NATO’s enduring support for Ukraine. He barely stuttered during his remarks as he pledged security guarantees from Western countries beyond the end of the war in Ukraine.

But that was quickly overtaken by a very embarrassing mistake.

As Biden introduced Zelenskyy to give his remarks, the U.S. president said: “Ladies and gentlemen, President Putin.”

Some of the 20-odd European leaders on stage at the ceremony began to clap, but others — unsure how to react to Biden’s error — didn’t do anything at all. An audible gasp was heard across the NATO press room.

Biden’s solo press conference at the end of the NATO summit has been seen as an important moment for him to assert his strength as a leader and prove that his presidential campaign can survive.

But with an intense focus on the president’s mental fitness following his disastrous debate performance late last month, the mistake will dominate the conversation following the end of the summit.

After recognizing his mistake, Biden attempted to laugh away the slip-up.

“I’m so focused on beating Putin. We gotta worry about it. Anyway…,” Biden said.

“I’m better,” Zelenskyy replied.

“You’re a hell of a lot better,” Biden said.