The sighting prompted the pair to embark on a three-month mission to study the fox and its habits.
The red fox is much more common in the UK
There have only been five confirmed sightings in Britain in as many years
After a tense wait, the fox appeared shortly after 11pm to eat food left out by Mr Burns.
Black foxes get their unusual colouring from a rare genetic defect, and are practically unheard of in Britain.
He said: “I was expecting the fox to be dark, but this one was as black as a labrador, with just the hint of silver highlights along its body.
“After a short while it just melted into the night. I felt so privileged.”
Martin Hemmington, of the National Fox Welfare Society, said: “There have only been five confirmed sightings in Britain in as many years.”
Urban foxes are now so prevalent that they are considered pests in some areas.