Prince William and Joe Biden once met in secret when the Duke and Duchess of Cambridge had their royal tour in the U.S. Biden was still the vice president at that time, who welcomed William with then-President Barack Obama at the White House in 2014.

According to Daily Express, Prince William had a very public audience with Obama at the Oval Office before he headed to New York City to meet up with Kate Middleton. After his meeting with Obama, Biden and his wife, Jill, hosted the Duke of Cambridge at a separate event.

Whatever they discussed was not known to the press as no journalists were allowed to join in. However, Daily Express speculated that Biden might have talked trade deals with the Duke of Cambridge for the European Union (EU), specifically for his Irish roots. The Cambridge couple's trip to the U.S. happened several years before Brexit so the EU was still on the table. 

But, William's meeting with Biden was of smaller importance than the meeting with Obama. Apparently, Obama's invitation to the Duke of Cambridge was seen as monumental because William was not going to be sitting on the throne for decades. 

Normally, U.S. presidents only meet with the sovereign, who is Queen Elizabeth, or her successor, who is Prince Charles. It was unprecedented to have the second in line to the throne at the White House. 

According to CNN, Obama likely invited William to his official residence to talk about illegal wildlife trafficking.  The press release of the royal's White House visit indicated that Obama welcomed William's work against this growing environmental problem. 

Six years after that White House visit and Biden is now the Democrat's choice for president in the coming U.S. elections this November. But, reports stated that William and the rest of the royal family are upset because Prince Harry seemingly made an indirect endorsement of Biden's candidacy. 

The royal family prefers to stay neutral or apolitical when it came to politics but Prince Harry has been quite vocal about the U.S. elections with his wife, Meghan Markle, who remains a citizen of the U.S. British folks are apparently not happy with the Sussex pair's meddling that 68 percent want them stripped off their royal titles. 

Meanwhile, a new book about Prince William and Harry uncovers more speculations about their highly-speculated rift. Biographer Robert Lacey wrote in Battle of Brothers: William, Harry and the Inside Story of a Family in Tumult that it's heartbreaking to dissect what really went wrong with this relationship. The book will be released on Oct. 15.