One of the beehives didn't make it through the winter

One of the beehives was struggling over the last few weeks and it was difficult to do a full inspection with the days being so cold. We could see it was weak and tried giving it some food to boost it. It was re-queened last August with a nice young queen from Keith and at the last inspection in late September it had 3 frames of brood and looked to be doing good.I have another queen from Keith that is doing great and was keen to get both of them through the winter and add some new genetics into my bees.When we eventually got to have a look through it last week we saw that there were drones hatching out of worker brood cells. This could have happened due to the queen running out of sperm and as a result only able to lay un-fertilised male eggs. Another possibility is that the queen died over the winter and workers started laying drone eggs.The picture below shows the remaining half hatched drones. They are normally reared in larger drone cells.