Fat is usually stored in the body in the form of triglycerids. When fat is used, it’s usually not turned into glucose, but rather into fatty acids, that are then released in the blood and reach the cells that need extra energy, where they are used by the mitochondria to power said cells. The signaling that triggers this is in fact done by a bunch of hormones that do indeed circulate in the blood to reach the cells specialized in storing fat, called adipocytes.
Depending of what triggers the transformation of fat into fatty acids( a process called lipolysis), those hormones could be insulin, epinephrin, growth hormone, etc.
That’s a french ‘Poilu’, a WW1 soldier. I’m pretty sure he would strangle you with his sausages if he heard you call him Hans.