In the FMA Brotherhood anime, Ling reveals himself to Ed and Al as a prince from Xing immediately after the scuffle with Lan Fan and Fu. But in the manga, Ling takes a bit longer to disclose that fact about himself.
In the manga, Ling brings up the details of his heritage for the first time after Al prompts him in this scene here, which was not included in Brotherhood:
We all know that life wasn’t rosy for Xing’s many royal half-siblings, who are all pitted against each other over who gets to succeed the throne. But it speaks volumes that even though Ling’s goal is to impress his father the Emperor enough to gain his favor, Ling very flatly states that he and his father have never even spoken with each other.
It makes me wonder if the Emperor interacted with any of his (43) children at all. And if so, which ones and why them? And what do the other siblings feel about their familial situation?
I think it’s interesting that Ling takes this fact very nonchalantly; he doesn’t seem pleased about it, but also doesn’t appear to have any strong feelings about it either. For him, it is what it is. In that way, it could be said he’s more like Al than Ed with regard to absentee fathers. Or he could just be hiding his feelings which would also be in character at this point since it seems he’s avoiding saying unnecessary information.
(side note but Ling’s “you guys are imagining all kinds of things about my life aren’t you” - WELL YEAH LING IT’S KIND OF HARD NOT TO WHEN THE INFORMATION THE PROVIDED ABOUT YOU AND YOUR COUNTRY IS SO SCANT. We fans are instead forced to come up with our own speculation.)