I have a Theory that might make sense to some. I Just finished watching season 5 of She-Ra and the Princesses of Power and they Explained the word GraySkull for every-time when Adora calls out "For the Honer of GraySkull" is basically a code word this was proven in Episode "Return to the Fright Zone" were Bows Fathers shout the words For the Honer of GraySkull witch shows the map to the Fall Safe that will unbound Ether's Heart and Restore the Magic to Ethera. and " Heart Part 1" Horde Prime Explained what happen to the "First Once" how he so called Defeated them but he also goes on that I have "Memory of it" Now here is my Theory because of Prime said "I Have No Memory of it" maybe that he was actually Defeated by King GraySkull him self and force to flea Eternia but only to Destroy whats left of its Mighty Empire including Killing GraySkull. So who is Mara the First She-Ra I think Mara is GraySkull's Twin Sister, and in act of Vengeance she and several of GraySkull's Army Followed her into Space seeking Revenge on Horde Prime. Knowing his Weakness is Magic they Sought out Worlds Rich in it to stop him but when they finally got to Ethera Mara had enough of it and rouse to stop her People from taking life away thus Mara saw that they became like Horde Prime and she said enough is enough and plunge Ethera into the Dark Dimension so her people cannot find it and use the Hart to kill everyone on Ethera!
May the Shwartz Be With You