Assembly Environment Minister Sue Essex was at the official re-opening ceremony on Pen-y-Fan, the highest peak in mid Wales, on 15 June - a day hailed as good news for the beleagured Welsh tourism industry.
Pen-y-Fan in the Brecon Beacons has been shut after a new case was confirmed on Modrydd Farm in Libanus near Brecon.
It was the first confirmed case in Wales for four weeks, during which many had been encouraged by the apparent retreat of the disease.
Assembly Environment Minister Sue Essex was at the official re-opening ceremony on Pen-y-Fan, the highest peak in mid Wales, on 15 June - a day hailed as good news for the beleagured Welsh tourism industry.
But the discovery of the disease in cattle on the farm came on the very day councillors were due to officially re-open all uninfected rights of way in Powys, and it will wipe away any complacency.
Cattle cull
The Farmers Union of Wales said it was a severe setback.
Pen-y-Fan was shut again on Saturday night by the Department for the Environment, Food and Rural Affairs and a cull of animals on six farms surrounding the new outbreak began on Sunday morning.
Officials will slaughter 2,000 sheep, 2,000 lambs and 159 cattle on the satellite farms. At Modrydd, 600 sheep, 600 lambs and 80 cattle were slaughtered immediately.
Pen-y-fan is one of the most popular and important peaks in the UK for walkers and it was hoped the lifting of restrictions in time for the summer season would benefit the tourism industry considerably.
Conservative assembly member Glyn Davies said the news was a very severe blow for tourism in paricular and he predicted more cases this week.
"One very worrying aspect is that the farmer involved has a couple of thousand sheep up on the hill," he said. "If it spread into a mountain flock, this could be a disaster.
"What they don't want is for there to be cases still in the autumn because it thrives in cooler weather."
The Wales Tourist Board estimated that £20m was being lost to the economy each week at the height of the foot-and-mouth crisis.
Powys County Council's rights-of-way committee has earlier given the green light to re-opening central areas of the Brecon Beacons National Park, including Pen-y-Fan and Llangorse Common.
Officers had erected 'Green for Go' signs on paths due for access on Saturday.
Powys is by far the worst affected Welsh area, with the latest outbreak taking the number of cases to 57. As much as 75% of the county is still an designated affected area.
The council estimates up to £50m could be lost by non-farming business in the county because of the disease and has asked the National Assembly for financial help.