Candid photos from President Joe Biden's visit with King Charles show the close bond the 2 leaders share

• President Biden met King Charles III at Windsor Castle on Monday during his visit to the UK.
• They were photographed laughing together and appeared animated as they discussed climate change.

President Joe Biden and King Charles III appeared friendly during the president's visit to the UK on Monday, forgoing formal greetings and laughing together at a welcome ceremony at Windsor Castle.

Biden met with the king and the UK's prime minister, Rishi Sunak, in a trip that the White House said was intended to "further strengthen the close relationship between our nations," Reuters reported on Sunday. Biden and Sunak will both attend the 74th NATO Summit in Vilnius, Lithuania, beginning on Tuesday.

Charles and Biden have met before on several occasions, including at the G7 Leaders Summit in Cornwall, England, in June 2021 and at COP26 in Glasgow, Scotland, in November 2021.

Here are the best candid photos from Biden's visit with Charles.

President Joe Biden touched King Charles III's arm as they shook hands at a welcome ceremony at Windsor Castle — a breach of traditional royal etiquette rules.

President Joe Biden shakes hands with King Charles III during a welcoming ceremony at Windsor Castle in Windsor, England, Monday, July 10, 2023.      Susan Walsh/AP

Biden also put his arm around the king in another non-traditional move.

President Joe Biden places his hand on the back of Britain's King Charles III as they return to the Dias after inspecting a guard of honour during a ceremonial welcome in the Quadrangle at Windsor Castle in Windsor on July 10, 2023.      KIN CHEUNG/POOL/AFP via Getty Images

Charles didn't seem to mind, returning the favor by touching Biden on the arm as they walked inside a tent for the ceremony.

President Joe Biden walks with King Charles III during a ceremony before their meeting at Windsor Castle in Windsor, England, Monday, July 10, 2023.      Kin Cheung, Pool/AP

After the president's arrival, Biden and the king watched a short procession of the Welsh Guards, a regiment of the British Army, before listening to the US national anthem.

King Charles and President Joe Biden inspect the Guard of Honour formed by The Prince of Wales's Company of the Welsh Guards at Windsor Castle on Monday.      REUTERS

As they departed the ceremony, Biden shared a joke with Charles' equerry Major Johnny Thompson, who accompanies the king at royal events.

President Joe Biden jokes with King Charles III's equerry, Major Johnny Thompson, after the ceremonial welcome in the Quadrangle at Windsor Castle in Windsor on July 10, 2023.      BEN STANSALL/POOL/AFP via Getty Images

Biden and the monarch appeared to enjoy each other's company as they smiled and laughed on the castle grounds.

King Charles III and President Joe Biden laugh in the Quadrangle at Windsor Castle on July 10, 2023, in Windsor, England.      Chris Jackson - WPA Pool/Getty Images

Later that day, Charles and Biden appeared animated as they spoke about climate change with philanthropists and investors.

President Joe Biden and King Charles III meet participants of the Climate Finance Mobilisation forum in the Green Drawing Room at Windsor Castle on July 10, 2023, in Windsor, England.      Andrew Matthews - WPA Pool/Getty Images