But organisers were happy that the Duke was able to spend nearly an hour viewing the reserve and talking to local dignitaries, guests, staff and volunteers.

He also seemed to have recovered well from a chest infection which caused him to be admitted to hospital in London for three days earlier this month. Pensthorpe's marketing and communication officer, Mark Noble, said: "The Duke seemed on really good form."

The visit was arranged because The Duke is patron of the Pensthorpe Conservation Trust and opened the nature reserve near Fakenham in July, 1988.

He arrived at about 3pm to be greeted by the owners of the reserve, Bill and Deb Jordan, and wildlife expert David Bellamy, who is chairman of the Pensthorpe Conservation Trust.

Mr Jordan gave The Duke and guests a presentation on the importance of the Upper Wensum Valley and the role of the Pensthorpe Conservation Trust in the area.

The Duke said he was pleased to have the opportunity to return after 20 years and see how the project had developed. He also recognised the key contribution made by the reserve to conservation on many levels.

Before leaving, he unveiled a commemorative plaque and cut an anniversary cake.

Mr Noble said afterwards: "The visit was an absolute success. The Duke got a good flavour of the place and we got across all the messages we wanted to convey. It was a shame he could not complete his tour but the heavens well and truly opened."

Pensthorpe is expecting another well-known visitor on Saturday, May 17, when a Wild About The Wensum event is due to be opened by singer and wildlife enthusiast David Gray.

For more on The Duke's visit to Pensthorpe, click onto our video slideshow.

Pictures by PAUL MARSH