Spoilers about shanks

hi everyone, i had a question regarding shanks. i’m catching up from reading ever since wano manga ended so my mind is sort of foggy. read all of egghead and now i’m on elbaf arc but i saw on twitter that shamrock was shanks’ twin brother? when was it ever confirmed that shanks was a figerland? i have no recollection of it at all and does that mean he’s a celestial dragon?