If my google-foo isn't failing me, uh... apparently there's a character in the SD Gundam Gaiden series (AKA the Knight Gundam series) called Knight Alex, who later on got brainwashed into Knight Alex Shadow/Knight Alex Shift or something and then later got sealed away in this thingamabob called the Armor of Sealing, which is the same thingy that G-Forest Goddess is currently stuck in.

Meanwhile the brainwashing mask is from SD Gundam Sengokuden (AKA the Musha series). I don't think it appears in the Gaiden "Knight" series, but I wouldn't put it past the SD series to have some sort of convoluted crossover event—

Dammit, G-Spring "Senjin" was right, SD is one big honking "swampy morass".