Which character is the youngest Shelby brother?

Finn Shelby is the youngest Shelby brother in Peaky Blinders.

Finn is the youngest son of Arthur Shelby Sr. and the younger brother of Arthur, Tommy and John; Ada is his sister. Unlike his older brothers, Finn is too young to serve in the First World War, an experience that shapes the returning Shelby men and helps explain why they often see him as inexperienced.

He grows up around the Peaky Blinders but is initially protected from their most dangerous work. As he becomes older, Finn joins the family business and participates in criminal operations, though his immaturity and appetite for partying repeatedly make him unreliable in the eyes of Tommy and Arthur.

The name Duke Shelby can cause confusion because Duke is also a younger member of Tommy’s family. Duke is Tommy’s previously unknown son, not his brother. Michael Gray is Tommy’s cousin and Polly Gray’s son, while John Shelby is Finn’s older brother. Finn’s eventual expulsion from the family in the finale underlines how far he has fallen from the Shelby inner circle.