Integration

[Balgus82]

It's not said in the actual show yet, but it is said outright in interviews.

"So the way we addressed that was to get away from him being the architect, or the scientist, of the series and tried to expand on his character. And the way we did that was we made him the adopted brother of Lion-O"

and

"Tygra's the older adopted brother and from everyone's point of view in the kingdom, he's the one who should be king."

Thunder Thursdays: Know Your ThunderCats! - TV Preview at IGN

Hope that will be proof enough to settle the dispute.