Prince Charles, Queen Elizabeth II’s heir apparent, has a complicated relationship with his father, Prince Philip. While the two royals are not really antagonistic toward each other, they’re not exactly the closest father and son pair as well.

But unknown to some royal family fans, Prince Charles and Prince Philip actually share the same passion — their love for the environment. While Charles may be more visible in his support for environmental causes these days, the Duke of Edinburg, who already retired from royal duties, is actually considered as one of the pioneers in environmental conservation.

For instance, Prince Philip founded the Australian Conservation Foundation in 1965. It is the nation’s first environmental organization and, more than five decades since its inception, is now the most prominent group dedicated to nature preservation in the country.

The Duke of Edinburg likewise cofounded World Wildlife Fund in 1961, the largest conservation organization in the world. Prince Philip is the group’s President Emeritus, which show’s his dedication and commitment to the cause.

Meanwhile, Prince Charles is also known for his focus on environmental sustainability. He founded the International Sustainability Unit in 2010 to help “address critical challenges to development and the environment.”

At the 7th International Green Awards in November 2012, Charles also received the Lifetime Achievement Winner award for his sustainability efforts in his own household. He installed solar panels at Clarence House and Highgrove and biomass boilers in Highgrove.

It is this passion for saving the environment that he sometimes received criticisms for. As a member of the royal family, he is supposed to remain politically neutral in public.

In a series of letters addressed to Tony Blair from 2004 to 2005, Prince Charles offered some suggestions on how to address climate change. “Energy efficiency could make a huge difference and would engage the public in the whole subject in a way that simply focusing on the industry's role will not,” the Prince of Wales wrote.

However, Charles’ action received mixed reactions. There were those who believe that there was nothing wrong with him sending those letters to the Prime Minister.

“The letters were very constructive, there was a purpose to them,” royal commentator Richard Fitzwilliams told DW. “Many of his views are now mainstream. And, he was offering advice, not issuing instructions that had to be followed.”

But there were those who believed that Charles breached the monarchy’s supposed political neutrality. “These environmental issues are complicated and contentious,” Graham Smith of the organization Republic explained. Smith believes that the Prince of Wales should just keep out of the issue.

Prince Philip once said that the difference between him and Charles is that the Duke of Edinburg is a pragmatist while his son is a romantic. But regardless of how they view the world around them, these facts show that both royals share the same passion for the environment.

Royal Family Britain's Prince Charles, Prince of Wales; Britain's Camilla, Duchess of Cornwall, US actress and fiancee of Britain's Prince Harry, Meghan Markle; Britain's Queen Elizabeth II; Britain's Prince Harry; and Britain's Prince Philip, Duke of Edinburgh, leave after attending the Royal Family's traditional Christmas Day church service. ADRIAN DENNIS/AFP/Getty Images