The Queen and Sir David Attenborough are to appear together in a documentary during which the monarch offers a rare glimpse of her humour.
Created by ITN Productions, the programme follows the progress of the Queen's Commonwealth Canopy project which was launched more than two years ago.
Part of the show will feature a unique and informal conversation between the Queen and the veteran presenter, filmed in the gardens of Buckingham Palace in the summer.
The short clip begins with the pair walking through the sun-drenched gardens of the royal residence as they discuss the Commonwealth Canopy project and its development.
As he happily chats to the Queen, Sir David says: "I suppose, actually, the trees with which you will be presented are going to change as our climate changes and there will be all kinds of different trees growing here in another 50 years' time."
In response, the Queen says: "It might easily be, yes. I won't be here though," causing Sir David to laugh at her quip.
The Queen's Commonwealth Canopy project was the brainchild of Labour MP Frank Field, who had a vision of creating a collection of forest and woodland conservation initiatives.
Across the 52 Commonwealth member states, these areas will be preserved in perpetuity to mark the monarch's lifetime of service to the family of nations.
Inspecting and discussing the various plant life, the Queen turns to Sir David and states how they "won't look at that one" as she highlights a tree that "does not seem to be doing very well".
Sir David can be seen chuckling heartily as he covers his face with his hand and the Queen addresses someone off camera as to whether the plant is "meant to be like that?"
"Somebody sat on it I think at a garden party", the Queen adds as the camera cuts to an image of the bent sapling.
Both aged 91 and born just a few weeks apart, they also share a moment over the issue of "health and safety".
As they are drawn to a chestnut tree, bursting with developing conkers, Sir David remarks how they are "not ready yet", and "hmm ... conkers".
The Queen then turns to him as they walk away from the tree and adds: "Was it recently that someone tried to stop children playing conkers?"
Sir David questions whether this was on the grounds of heath and safety, to which the Queen confirms it was.
Sir David notes: "You'll think that people will stop people breathing."
Prompting a small chuckle from the Queen, she adds: "It seems to be quite a harmless battle thing."
:: The documentary, set to be called The Queen's Canopy (working title), will be screened on ITV next year.