EXCLUSIVE: Never-before-seen pictures of secretly pregnant Marilyn Monroe, who confided to her close friend that co-star Yves Montand was the baby's father - not husband Arthur Miller

Marilyn Monroe's friend Frieda Hull kept the color pictures she took of Marilyn's baby bump private; they were sold as part of Frieda's estate last year. The pictures were taken in July, 1960 in New York City; Marilyn was 34 years old. Marilyn and married French actor Yves Montand began working together on Let's Make Love in February of that year and their affair began a month after. These images were the prized possession of Hull, who worked for
Pan Am and became close to the star while part of a group of fans known as the Monroe Six. Frieda dubbed the pictures 'the pregnant slides' - a reference to a shocking secret the screen siren kept right up until her death. Tony Michaels, a friend and neighbor of Frieda's, bought the images at the 'once-in-a-lifetime' Marilyn Memorabilia Auction held by Julien's Auctions in LA..As to what happened to the pregnancy, Michaels told DailyMail.com: 'All Frieda told me was that Marilyn has lost the baby, it was never made clear whether that was by way of a miscarriage or even an abortion, and I never thought to press her on it.'