The two Royal Sisters ruled Equestria. They were its Protectors, its Guardians, its leaders, selected by the three tribes. Starswirl the Bearded, he was their mentor, he was there to guide them, he was there to counsel them. Perhaps, they may even view him as their father-figure. Many believed them to be true.
This was not entirely the case.
The Royal Sisters past is something none would venture on to question, how were their life before becoming a Princess, what feat of events that awakened the hidden powers within them? None would know except the King.
Now, the King, the true Guardian of Equestria, has returned. They were bound, not by flesh, but by the bond they shared. He shall return as promised.