Two yolks in one egg

Screenshot_20180315-125845.pngPreparing breakfast this morning.... Just needed few slices of 🍞 bread, some eggs and a cup of 🍵 tea.... So I took a walk to my kitchen... Got Two fresh eggs.... Picked my fork and break the egg into the plate.. And I discovered two yellow yolks in one egg...................please steemers how can this be explained biologically....