Board Thread:Manga/@comment-39923830-20190624210314/@comment-25933225-20190624222502

Well, it's hard to confirm it or not. You'll see, what I'll say is mostly analyzing and suppositions, so I'll use a lot words like "could", "might".

Grisha ate the Founding Titan, that was also Frieda Reiss, a member of the royal bloodline. So, in this particular case, he's eaten the Power of Titan AND a member of the royal family. Was he able to use the power of the Founder? Well, we will never know, as he didn't try.

If Eren ate Historia, will he be able to use the power of the Founding freely? Hard to say. This case isn't identical as the one we had with Grisha, as Eren received the Power from someone who didn't have royal blood. If Eren ate Historia, he MIGHT be able to use the Power of the Founding... At least for the time of the transformation. Hard to say if this ability will be kept once he goes back to humain form: it's the Titan's body that ate Historia, not Eren himself. Back to human form, he wouldn't have any contact with royal blood anymore, so he might not have the full Founding Titan's power.

And, as specified in the manga and the anime, Eren was able to use the power of the Founding when he touched a TITAN of Royal Blood (Dinah Fritz). The fact that it has to be a Titan (and not simply a person of Royal blood) is now a lore information, but it might have been introduced as a plot device to justifiy why Eren can't use the Power of the Founding Titan every time he touches Historia.

Here, we bring the question of Zeke. We don't know if Eren can activate the power of the Titan while touching Zeke in human form. I think it might work. However, in Beast Titan form, that'll work for sure... For a short time of course. Now, if Eren ate Zeke? Well, he will inherit of the Beast Titan, we'll get some hairy-Attack Titan. But will he be able to use entirely the power of the Founding? Well, he will be able (for sure) to use it for a short amont of time at least because Zeke is a royal blooded Titan. However, like Historia, we don't know if the effects of this will go one after Eren comes back to human form, as it's the Titan who ate Zeke and not Eren himself.

However, as Eren gained the Power of the Beast Titan, he will still keep something from Zeke from eating him, unlike with Historia. But will this "thing" be enough for Eren to keep the Founding power's active? We can't say.

All of that was theories, suppositions, based on a few lore-facts, but as we miss other lore-facts (eating a member of royal blood, eventually a Shifter, will iit allow Eren to use the Founding for ever?) we can't go further than theories.