What did historia give birth to a titan shifter?

I am not that well versed on the lore and story of attack on titan, but in the final episode we see a shot of what seems to be queen historia giving birth to a child, right as eren gets blown up. At first I thought that this was the beast titan being reborn, which would be fitting as originally queen historia was supposed to inherit the beast, but the placement of the shot makes me belive that when eren was blown up, a part of the founder Yimir died as we see a representation of her on Erens spine, what if the titan that was reborn was the founder and not the beast,

(The brainrot may be getting to me guys, I just think this because of the shot placement)