Tim Rooke / REX / Shutterstock / Rex USA 1 / 3
Tim Rooke / REX / Shutterstock / Rex USA 1 / 3

During the Queen's 90th birthday celebrations, an adorable friendship stole the spotlight from Queen Elizabeth II. Seen giggling together and sharing jokes, it was clear Prince Harry and Duchess Kate have really developed a close bond.

According to the Daily Mail, this friendship has really deepened over the last five years of being in-laws. Their sources close to the castle assert that Duchess Kate is Harry's closest female friend these days, beating out cousins and other gal pals.

But how did these royals reach bestie status? There wasn't always an ample amount of love between the two. Once upon a time the handsome prince wasn't wholeheartedly behind his brother's choice of a future Queen.

The royal couple started dating in 2003, but broke up briefly in 2007. Their split made major news, as everyone wanted to know what went wrong. British outlet Evening Standard asserted that Prince William's friends weren't keen on Kate, and that Prince Harry sided with William's friends who called her "the limpet." (For the non-Brits, that term equates closest to referring to Kate as a clinger.) The publication cited a source that explained Harry "felt Kate enjoyed her fame-by-association a little too much."

Nowadays, it's hard to imagine Harry speaking anything but Kate's praises. The two reportedly get on famously, and spend tons of time together according to the Daily Mail's insiders.

Among one of their favorite things to do together? Watch "Game of Thrones," of course! "Theirs is a genuine friendship, founded on nights spent in front of 'Game of Thrones' boxsets and companionable suppers," one source shared. "From giving him cookery lessons to offering sensible romantic advice, Kate has become Harry's lynchpin."

The siblings-in-law are currently neighbors, as Prince William and Duchess Kate live in Apartment 1a and Prince Harry resides in Nottingham Cottage, mere feet apart from one another on the Kensington Palace compound.

This proximity has only helped their relationship, as Harry reportedly spends a lot of time at his big brother and sister-in-law's place. The handsome royal pops over for family dinners, and makes an effort to spend plenty of time with his niece and nephew, Prince George and Princess Charlotte.

Here at Wonderwall, we're all for a close relationship between the good-natured royal and beautiful future Queen! We just have one question -- can we come over for "Game of Thrones" next week, guys?