Prince William celebrated his 40th birthday on Tuesday, June 21, and his wife, Kate Middleton, wanted nothing but for him and Prince Harry to mend their relationship. The Duchess of Cambridge believed their reconciliation would be the "best birthday gift ever" for her husband.

Prince William and Prince Harry's relationship has been strained since the former showed concern over his younger sibling's fast-developing romance with Meghan Markle. Since then, a lot has happened, leaving their relationship hitting rock bottom.

The second in line to the throne celebrated his big day with his loved ones. However, despite the happy occasion, the future queen consort is reportedly heartbroken that her spouse will once again celebrate his birthday without his one-and-only sibling.

Sure, he received a lot of good wishes and congratulatory messages from other royal family members, but none of them came from Prince Harry. That said, it shows that the rift between the two princes is still ongoing.

A royal source said, via Express, that Kate Middleton had been urging Prince William and Prince Harry to settle their differences as the future king turned 40.

The insider continued that the duchess felt nostalgic on the prince's birthday, knowing they celebrated his 30th in 2012 with a special trip to Whales, where the two brothers had a great time bonding.

The tipster even revealed that she "quietly sent a message" to Meghan Markle's husband that it would mean a lot to his older sibling if he would contact him on his big day. Being a diplomat and an optimist, she reportedly believed that Prince Harry would "snap out of his trance and be his own man."

"If she can somehow get the boys to make peace-even temporarily-it would be the greatest birthday gift William could wish for," the source said.

Kate Middleton has been receiving heaps of praise for being a "solid impeccable" wife to Prince William, per People. Many believe he has the best partner in life as they are set to face the next decades together for the monarchy.

However, it is with deep sadness that he has lost one partnership with his brother, Prince Harry. With their ongoing estrangement, it looks like it will still take time before they finally mend their relationship. As this feud continues, it is reportedly the source of pain and hurt not just for Prince William but also their father, Prince Charles.