Where did we learn this canon fact?

Besides the dual stream confirmation in Discovery, I believe it’s in Enterprise that we first learn that Klingons have two of every organ.

And I believe I recall a throw away line of confirmation (of the double organs) in Picard.

I’m honestly surprised if Lower Decks hasn’t dealt with the topic yet.

Klingons have two of every organ.

The Skin is an organ, not just an organ but the largest organ.

That explains the facial folds.

Not canon, but there was a fan theory that the changes occurred after the tribbles were transported aboard the Klingon ship in TOS.

They retconned the TOS Klingons in Enterprise

…wikipedia.org/…/Affliction_(Star_Trek:_Enterpris…