The Bidens paid their respects to the queen as she lay in state in London.
The first lady and the U.S. ambassador to the U.K. stood silently with Biden and his hand over his heart as he made the sign of the cross.
Biden told reporters after visiting the coffin that the queen was decent, honorable, and all about service, and even in private reflected the image she'd portrayed in her 70 years on the throne.
The president was among thousands of mourners who have streamed past the coffin in recent days.
Olena Zelenska, the wife of Ukrainian President Volodymyr Zelensky, visited the coffin on behalf of her country after meeting with Prince William's wife.
European Commission President Ursula von der Leyen, Japanese Emperor Naruhito, King Felipe VI of Spain, and Queen Letizia of Spain were all photographed arriving at Buckingham Palace for a diplomatic reception hosted by the new monarch King Charles III.
Thousands of people lined up for hours over the weekend to view the queen's coffin at the oldest part of the Houses of Parliament. David Beckham was one of the celebrities who waited hours to pay respects. Thousands of people are expected to attend the state funeral of the queen at the abbey.