[@ViolentViolet]

I already stated in one of my in-character posts the rest of the Kingsguard knows about it. It is a common theme within the Song of Ice and Fire, the Kingsguard have three utilities. Protect the King, gight his Battles, occasionaly offer advice and keep his secrets. That also extents into the circle of the White Brothers.

For example, everyone in the Kingsguard of Aerys the Mad knew that one of them, Prince Lewyn Martell, kept a secret lover. I am just aking so it doesn't cause any problem with the plot.