The Duke of Edinburgh took an early interest in conservation and remained passionate about animals and the environment.
Dr Claude Martin was the director of the WWF in Switzerland from 1980 to 1990 and then Director General of the WWF internationally from 1993 to 2005.
Here, he tells Sky News about the role Prince Philip played as president of the conservation charity between 1981 to 1996.
I knew Prince Philip since 1981 when I was still director of the WWF in Switzerland. He became president of it internationally, and when I was director general of the whole of the WWF he was my direct boss until 1996.
I travelled a lot with him and went to many countries with him, visits for conservation work, and I came to know him quite well.
He had a genuine interest in conservation. It was at least 1956 when he became interested in conservation, I think it was the contact with Peter Scott, who founded the WWF, that had an effect on him, and an influence on him and his understanding.
Since he was in the Navy, he started getting interested in birds, there must have been something from childhood, that was not the only a trigger for him but that made him interested in the world.
It is not a surprise that Peter Scott became known to him - he had an interest not just in horses and the equestrian worlds, which he was interested in before WWF.
He took an interest in nature and I think the interest was always with birds but was also with fisheries - I remember having many discussions with him about fisheries.
The WWF programme on fisheries clearly goes back to him. He had a concern about captive bred salmon, and them mixing with wild salmon.
There was a considered thinking behind what he said about these things.
Something that had an impact on me was his visit on his own to the education centre we were running in Switzerland.
We also ran an interfaith evening, and that was historical - it led to the Assisi Declarations on Nature.
That was his idea - reaching out to those who should naturally be involved and get their commitment.
That was the centre of the Assisi declaration, that went back to him.
He thought about getting that idea of conservation out to other people who were not easily accessible to us.
He didn't lead on climate change but he never denied it.
He definitely did bring these views to the public in the early 1990s. He went to the World Economic Forum and talked about conservation.
And that was when these business people were not particularly interested in conservation, and he came there as a president and talked to the WEF about the need for businesses to take care of natural resources and nature.
That was daring at the time, that people even denied that climate change was happening. It was very different times.
That was not the thinking of the business people in the early 1990s. I think he played an important role in putting this on the world agenda with heads of state as well.
At times this was interesting - the response they had - at times it was frustrating, or non-committal.
In other cases it was, "Here comes the husband of the Queen of England, and says this is important, you can't put this away".
He was the first and he played an important role.