Wagner, 74, said he was 22 when he and Stanwyck began their five-year affair, a relationship considered taboo because the legendary actress was 45 at the time, World Entertainment News Network reported Thursday.
"It was not public, it was hidden. It just couldn't come out. Today, it wouldn't have made any difference. Then it made a difference and it made a big difference for her," Wagner said.
The actor decided to speak of the romance because of a forthcoming book about Stanwyck, in which Wagner discussed the love affair.
"She was an absolutely wonderful, wonderful woman and it was so great for me. I loved her very much ...," Wagner said.
Stanwyck died in 1990 at age 82.