To celebrate its famous calendar's 50th anniversary, Pirelli pulled an unreleased 1986 calendar to publish for 2014.

In the words of Pirelli, "The Calendar is the icon of Pirelli's communication." "The Cal," as it's also referred, first came out in 1964 and featured artistic portraits of women, often wearing very little or no clothing. Over the years, the risque images have struck a chord in people around the globe, and many consider it the world's most famous calendar. (According to Autoweek, when a complete set of Pirelli calendars was put up for auction in 1975, the winning bid was more than that of an Andy Warhol painting sold at the same auction!)

To celebrate The Cal's 50th anniversary, Pirelli didn't release a 2014 edition, but instead pulled photos from its archive that were shot by the late Helmut Newton for the 1986 edition. Newton's calender and photos were never released. That year, Pirelli published a calendar with photos by Bert Stern instead of Newton's when his work started to slip behind schedule. Far from a distant second-choice photographer, Stern was famous for his shots of Marilyn Monroe.

Through its 50 years of existence, there have been ups and downs for The Cal, notably in the period from 1975 to 1983, when it wasn't published. But from 1984 to today, Pirelli has been churning out The Cal on a yearly basis.

Photographer Peter Beard attributes the staying power of the famous calendar to this: "The last thing left in nature is the attractiveness and beauty of women." Do you agree?

Head below to watch a history of The Cal, as told by the many photographers and models who have been associated with it, and to see Newton's portraits for the 2014 edition. Please note that the imagery may not be safe for work.