The show has hinted at the existence of a fourth Dutton brother in the past.
Fans have speculated that the fourth brother could be introduced to cause conflict or shake things up among the Duttons in future seasons.
Some viewers theorize that Kayce is actually the adopted son of John Dutton,
If there is another Dutton brother introduced in season 6, details about where he’s been and why he’s been absent from the show so far would likely be explained.
The arrival of a fourth brother could align with the show's themes of family drama
Assuming the fourth brother does get introduced, speculation over which well-known actor might be cast in this key role is likely.
While still unconfirmed, the groundwork for bringing a fourth Dutton brother onto Yellowstone in season 6 seems to have already been laid through small hints dropped in previous seasons.