In 1988, HRH Prince Philip preached a sermon as part of a four-part series of services on religion and belief broadcast by BBC Radio 4.
Tomorrow FaithInvest CEO Martin Palmer will be drawing on that sermon when he takes part in BBC Radio's coverage of the Duke of Edinburgh's funeral, which will form part of the official record of the occasion.
'It is the most explicit outline of his beliefs I believe he ever produced. I also believe this was his one and only sermon and it was done as an act of kindness to me!' says Martin.
In the sermon, written for the Christian season of Advent, the period just before Christmas, Prince Philip talks about the cycle of life and death, and expresses his concern about what humanity is doing to the planet.
'What believers in all religions ought to know, and what we seem to have forgotten, is that God has put limits on the endurance of all natural systems. The evidence is mounting that the human species is stretching those limits to the point of breakdown,' he said.
'Advent reminds Christians that there is the hope of spiritual re-birth at Christmas; it should also remind us that humanity is part of the natural order and it is our responsibility to give all life on earth that same chance of renewal and re-birth.
'It ought to remind us that we have no right to exploit it selfishly and ruthlessly. We are partners with all life on earth and joint beneficiaries of God's gifts of the life-giving air, water and soil.'
The sermon was published by WWF in a booklet entitled Advent and Ecology. You can read it in full here.
Since Prince Philip's death was announced a week ago, there has been a huge resurgence of interest in his pivotal role in inspiring faith groups to take environmental action themselves.
In the 1980s, Prince Philip as WWF International President convened a meeting between faith leaders and key environmental organisations: it was the first time the two groups had met, and for many faith leaders, the first time they had considered the environment as a religious issue.
'It was his absolute conviction, when it was not fashionable to have such a conviction, that religions are vital forces for a sustainable planet, and that secular environmentalists needed to work with them,' says Martin.
'Since then, all the major faiths have declared the environment to be a faith issue and now have programmes of practical action on the environment. Much of that would never have happened without the explicit support of Prince Philip.'
Indeed, FaithInvest itself was inspired by the Duke of Edinburgh's observation several years ago that the faiths could use their assets – their land, buildings, pensions and investments – to drive positive environmental action.
To find out how Prince Philip became the inspiration for the largest civil society movement on the environment, that of the faiths, see our Tribute Page.