US President Joe Biden touched down at Windsor Castle on Monday for tea and climate change talks with King Charles III. Biden, 80, was greeted by a band of red-jacketed Welsh Guards and the two inspected the troops before disappearing inside.

This was Biden's first meeting with the British monarch since his coronation in May. First Lady Jill Biden was also in attendance, having previously been at the state funeral of Charles's mother, Queen Elizabeth II, in September last year.

Biden, a longtime environmentalist, considers Charles a "clarion voice" on climate change, and the meeting was attended by top financiers and philanthropists to discuss climate finance. The UK government noted that more than $1 trillion is needed by 2030 to help developing economies get on track to reach net-zero carbon emissions by 2050.

Biden then left for a two-day NATO meeting in Vilnius, Lithuania, before heading to Finland for a US-Nordic Leaders' Summit. At the NATO meeting, the US and other Western allies discussed Ukraine's bid to join, as it is still at war with Russia.

Though the US is the most hesitant nation, it is seen as likely to drop the Membership Action Plane requirement for Ukraine's application. Before leaving for NATO, Biden held a garden meeting with UK Prime Minister Rishi Sunak for just under 40 minutes, discussing the need to strengthen their alliance and maintain their support for Ukraine, as well as economic ties.

The two have had a number of meetings in recent months, improving transatlantic ties strained by the past tenures of Boris Johnson and Liz Truss. Biden acknowledged the strong relationship, saying “our relationship is rock solid.”