President Biden appeared to forget the name of Australian Prime Minister Scott Morrison during a joint press conference Wednesday evening, calling him "Mr. Prime Minister" and "that fellow Down Under." 

Biden announced Wednesday a trilateral security partnership with Britain and Australia, called AUKUS, which includes the sharing of advanced technologies, like artificial intelligence and the acquisition of nuclear-powered submarines, among the three countries.

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The president gave a joint press conference with U.K. Prime Minister Boris Johnson and Australian PM Scott Morrison joining virtually on two television screens.

"Thank you Boris," Biden said to the British PM before turning to Morrison.

"And I want to thank that fellow Down Under," the president said, pointing to the Australian PM. "Thank you very much, pal. Appreciate it, Mr. Prime Minister."

Biden later addressed Morrison by name when reading off his teleprompter.

"As Prime Minister Morrison and Prime Minister Johnson said, I want to thank you for this partnership, your vision as we embark together on this strategic mission," the president said. "Although Australia, the UK and U.S. partnership — AUKUS — it sounds strange with all these acronyms, but it’s a good one, AUKUS — our nations will update and enhance our shared ability to take on the threats of the 21st century just as we did in the 20th century: together."

Prominent Australian news outlets like The Australian and Sky News pounced on the gaffe, and #ThatFellaDownUnder became a trending topic on Twitter.

Morrison didn’t acknowledge the slip-up but hailed the agreement as a "forever partnership for a new time between the oldest and most trusted of friends."

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"A forever partnership that will enable Australia to protect our national security interests, to keep Australians safe," he said. "And to work with our partners across the region to achieve the stability and security of our region."

"We're opening a new chapter in our friendship," added Johnson. "The U.K., Australia and the U.S. will be joined even more closely together, reflecting the measure of trust between us."