Queen Elizabeth II is set to host US President Joe Biden and Jill Biden at Windsor Castle this weekend. 

Joe is the 13th American President to meet the Monarch, who has always hosted every head of state since 1952.

One person who will be disappointed to miss Dr. Biden is Prince Harry, with whom he reportedly has a special relationship.

According to The Sun, the dad-of-two is close to the 70-year-old doctor after striking up a friendship after his US tour in 2013.

The Duke of Sussex and Jill first met each other at a reception for British and American wounded soldiers in Washington when Joe was still Vice President for Barack Obama.

After that meeting, Prince Harry and Jill met up several more times on different vital occasions. One time, the POTUS' wife even attended two of his Invictus Games in 2016 and 2017.

During the latter, Prince Harry first stepped out with his Hollywood star girlfriend, Meghan Markle.

They also often see each other a couple more times and have been spotted joking with each other and laughing around.

According to the Duke's royal biographer Angela Levin, they both get on brilliantly despite their 33-year age gap.

It has become frequent that even Joe admitted that his wife is "spending too much damn time with Prince Harry."

But what Prince Harry and Jill Biden bond most on is their military ties.

Jill's step-son Beau, a former army major, passed away in 2015 from brain cancer. Meanwhile, Prince Harry served in the military and even had British military titles given to him.

Twitter Error

READ ALSO: Lilibet Diana Not Named After Queen Elizabeth II? Meghan Markle's Former Pal Reveals Truth

How Close Are Prince Harry and Jill Biden?

According to body language experts Judi James, Prince Harry, and Jill Biden show a strong body language signal of a genuine and easy-going relationship.

She further said that Mrs. Biden has also shown a "tendency to stay very grounded," "warm," and can treat the Duke of Sussex as a "normal young guy rather than a royal," which also allowed him to relax in her company.

Aside from that, Jill also shares her space with the Prince.

Meanwhile, when he's around Jill Biden, Prince Harry's body language is said to be "awed" by the mother figure that he always grins "like a young schoolboy."

They also have two things in common - both are described as "rebellious" and "pranksters" during their younger years.

READ MORE: 'The Crown' Update: Netflix Show Faces Hurdle in Casting For Prince Harry, Prince Andrew Roles