A thin layer of fog blotted out the Sun on this morning but it didn't last long. It was a radiation fog which is caused by low level cooling at ground level. The fog forms due to the cooling which condenses water vapor into tiny droplets of water. The fog formed after sunrise so it did not have time to deepen. As the Sun rose it heated the ground which heated the air where the fog formed and the fog dissipated.
This is a different situation than the altostratus below. Altostratus is formed when condensation aloft is triggered by a layer of moist air rising in upward motion ahead of the storm system. The Sun does not burn off altostratus. The rising motion would need to be replaced by sinking motion - which warms the air causing the cloud to evaporation.