Was this TwinSoul's first appearance?

[Berlyn he/him]

I've read almost everything (haven't read White Sand) there is to read in the Cosmere, but I am just wondering if this was TwinSoul's first appearance in the Cosmere or if I have missed them in another book or series?

[Govir]

As far as I’m aware, this is his first appearance. I heard from one of the Shardcast episodes that this was Brandon playing with doing a crossover of a different series *before* that series came out. Not sure if TwinSoul will be a character in any eventual Aether books (not sure if I’m spelling that correctly, audiobook listener)

[Rorzikel]

TwinSoul is an entirely new character in both published and unpublished books. Never been seen before.