[Sword & Shield] What is the lore on Regidrago?

I know that according to the Pokemon Lore, Regigigas created the Regi trio from materials that it found. But was Regidrago also created by Regigigas? If so how did it create it since if we go by the name, it is a dragon type, did Regigigas find an ancient dragon pokemon skull to create it? I am really curious about it since it does not fit with the other Regi's or Regigigas that much.

Edit: Just found out about RegiEleki, and now I am even more confused about how that one was made.

According to what I heard, that thing was formed with 'dragon energy'. I don't get it either.

^Yeah, it's confusing. All I can assume is that the dragon skull is a Charizard skull? Maybe Mega Charizard X...? It matches a lot in color scheme, and the overall head shape is very Charizard-like too. Plus it's a dragon type, so I can see 'dragon energy' being taken from it somehow. Possibly when it mega evolves, since I imagine it'd have released a lot of energy at that point. Dark to think of the possibility that Regigigas killed a Charizard and made use of its energy in that way, as well as taking its skull.

Moved this over to SwSh too, since Regidrago theories/discussions would fit a bit more here.

see this is what bugs me about these two. i don't hate the new regis but i'm having a difficult time warming up to the two bc the lore about the regi trio was already really good. they're my favorite trio so i suppose it's natural i would have resistance to new ones many many years later. i can accept regieleki, but like you, i'm completely lost in the regidrago lore. like how did it happen. what's dragon energy. which pokemon had to die for this bc like how do you make a pokemon out of Dragon Energy...i