Robert Wagner's marriage to Natalie Wood was known to all. His love affair with Barbara Stanwyck was a secret — until now.

In his new memoir "Pieces of My Heart," Wagner writes of his four-year romance with the star of such classics as "Stella Dallas" and "Double Indemnity." They met on the set of "Titanic," released in 1953, when he was 22 and she 45 and divorced from actor Robert Taylor.

The press knew nothing about their relationship, and neither did most of Hollywood, except for such friends as Nancy Sinatra, the first wife of Frank Sinatra; and Spencer Tracy, whose bond with Katharine Hepburn was the ultimate show-business secret.

"I would say she gave me self-esteem," writes the actor whose successful TV series included "It Takes a Thief" and "Hart to Hart," but the relationship didn't hold. They were both too busy working, and the age difference was too great. Stanwyck eventually broke it off.

"I would always have been Mr. Stanwyck," Wagner, now 78, writes, "and we both knew it."