Which son of Doran Martell was sent to Daenerys and omitted from the show?

The son of Doran Martell sent to Daenerys and omitted from the show was Quentyn Martell.

Quentyn is Doran’s second child and eldest son. In the novels, Doran secretly sends him to Essos with the mission of marrying Daenerys Targaryen and bringing her support, dragons, and a possible alliance with Dorne. Quentyn travels with companions from House Yronwood and eventually reaches Meereen after a difficult journey.

Daenerys rejects his marriage proposal because she is already committed to another political arrangement. Quentyn then attempts to prove his worth by trying to claim one of her dragons. The attempt ends catastrophically: he is burned and later dies from his injuries. His chapters in A Dance with Dragons provide a tragic view of how Doran’s careful plans can fail.

The television series removed Quentyn completely and simplified Doran’s family to Arianne’s absent counterpart and Trystane. Oberyn and Doran appear on television, but neither is the son sent to Daenerys.