Everybody who ever watched 'The Big Valley' knows that Tom Barkley, the deceased patriarch of the Barkley clan, was a horndog. He had an illegitimate son named Heath by an Indian woman who was accepted into the family. (I'm not sure if we ever found out if that had been a loving relationship, or the result of a one-night stand... heck, for alls I know, it could have been rape!)
Tom Barkley cheated on his wife Victoria once; who's to say he didn't do so other times as well, all over the American West?
Perhaps even south of the border.....? In a small village just over the border in Mexico which served as the base of operations for General Arriola's sorties against US forts, undercover spy Jason McCord made first contact with one of Arriola's men, a thuggish bandito named Crispo.
Because of his similarity in appearance to Nick Barkley, it will be my assertion that Crispo was the bastard son of Tom Barkley by some Mexican peasant woman. Crispo was finally captured by US troops and was more than likely hanged for his crimes, including the murder of Colonel Harry Snow. He probably went to the gallows never knowing that he may have been the son of Tom Barkley. But then, he probably would not have cared...... (For those not familiar with the Toobworld concept, this is just a "splainin" as to why both characters - both of whom were played by Peter Breck in the real world - looked similar within the reality of the TV Universe.)