On 4th August 2020, while examining a series of artificial nestboxes for second broods of House Martins Delichon urbicum at an upland farm in north Northumberland, I found a full-grown juvenile sitting on a nest containing three eggs and one recently hatched young. The box had previously been used by a pair of House Martins to raise three young, which were ringed and fledged on or around 4th July. The bird found sitting on the nest was one of these fledged young.