Biden lavished praise on the 95-year-old British monarch after their private meeting which came at the conclusion of the Group of Seven leaders' summit at which he called for concerted action on China and ahead of a meeting with Putin on Wednesday.
"I don't think she’d be insulted but she reminded me of my mother, the look of her and just the generosity," Biden, 78, told reporters shortly before departing London.
"She's extremely gracious, that's not surprising, but we had a great talk. She wanted to know what the two leaders that I -- the one I'm about to meet with, Mr Putin, and she wanted to know about Xi Jinping, and we had a long talk."
The monarch, attired in a bright pink floral outfit, had warmly greeted Biden and his wife Jill in the Quadrangle of the castle, home to the royal family for nearly 1,000 years, where they were treated to a taste of British pomp.
The president inspected a Guard of Honour formed of The Queen’s Company First Battalion Grenadier Guards, which gave a Royal Salute, and the U.S. National Anthem was played before they entered the castle for tea.
"I said I wish we could stay longer, maybe we could hold the cars up a minute, and stuff. Anyway, she was very gracious," said the president who confirmed he had invited the monarch to the White House.