Queen Elizabeth reportedly wrote a private letter to Joe Biden ahead of his inauguration as the new President of the United States, according to Buckingham Palace.

Though the letter's content was not divulged, royal correspondent Chris Ship posted on Twitter that Queen Elizabeth wanted to congratulate Biden as the incoming American leader.

Biden will be the 13th U.S. president to be inaugurated during the Queen's long reign. Historically, Her Majesty has never shown her political colors as she has to uphold neutrality.

However, she has always maintained a good relationship with all U.S. presidents, including Donald Trump. During the State Banquet of Trump's visit to the United Kingdom in 2019, Queen Elizabeth told him that she looks forward to the future with the support of Britain's U.S. allies. Trump, on the other hand, had nothing but good words and respect for the monarch.

Queen Elizabeth has met all U.S. leaders in person, except President Lyndon B. Johnson. According to reports, Her Majesty and Johnson constantly corresponded from 1964 to 1967, but both parties never extended an invitation to visit each other.

Historians do not know the specific reasons for the lack of invitation, but the Queen did meet former First Lady Lady Bird Johnson during the monarch's visit to the United States in 1991. Then-Vice President Johnson also didn't get to meet the monarch during the state funeral of President John F. Kennedy because she was unable to travel. The Queen was pregnant with Prince Edward at that time.

Meanwhile, it's still unclear if Queen Elizabeth and Biden will meet in person in the near future. Travel plans are still uncertain due to the coronavirus threats. According to Daily Express, Biden might have a State Visit to the U.K. in 2022as the Queen will likely no longer travel to America in her old age.

However, one member of the royal family is good friends with Biden. Queen Elizabeth's grandson, Prince Harry, has personally spent time with the new POTUS and his wife, Dr. Jill Biden, because they support the Invictus Games.

The president's wife and the Duke of Sussex first met nearly 10 years ago. Harry felt an instant connection because the Bidens had a son, Beau, who was also a former military serviceman just like the Queen's grandson.

During the last U.S. elections, Queen Elizabeth was allegedly pressured to discuss Harry and Meghan's political leanings as they encouraged Americans to vote. Though they didn't name the candidate they support, many royal fans assumed that the Sussex pair supported Biden's campaign.