On Peyton Place, what was Rodney Harrington's relationship to Steven Cord?

They are half-brothers.

https://en.wikipedia.org/wiki/Peyton_Place_(TV_series)

They were half-brothers.

For two years, Rodney could not decide whether to be with Allison, the girl he loved, or Betty, the girl he married. In 1966, Mia Farrow left the series to focus on a film career and her recent marriage to Frank Sinatra. With Allison's mysterious disappearance, Betty more or less was allowed to have Rodney, since her main competition had left town. Betty eventually divorced Rodney, married dark and handsome attorney Steven Cord (James Douglas), then divorced him and re-married Rodney, in keeping with the convoluted lifestyles of these small town inhabitants. The rivalry between Rodney Harrington and Steven Cord was intensified by the fact that they were actually half-brothers. Though raised by Hannah Cord, Steven was actually the illegitimate son of Catherine Peyton Harrington and Hannah's husband Brian.

https://en.wikipedia.org/wiki/Peyton_Place_(TV_series)