A vintage wristwatch could become the world's most expensive Rolex ever sold at auction. The 1971 Rolex Daytona Reference 6265 crafted in 18-karat white gold is the only one of its kind and considered to be so rare it's been nicknamed "The Unicorn."

Phillips in Association with Bacs & Russo

Kevin O'Leary, star of "Shark Tank" and an avid watch collector, was given VIP access at Phillips auction house in New York to try on the iconic Rolex. O'Leary's initial reaction: "It's gorgeous." "It is truly a holy grail piece … the only manually wound, vintage Rolex Daytona made in white gold," said Paul Boutros of Phillips in Association with Bacs & Russo. Made in 1970 and then sold to an important German retailer the following year, Phillips told CNBC that at the time, the watch was probably the most extravagant model of the Daytona series ever created by the luxury watchmaker. The vast majority of Daytonas from this era were crafted in stainless steel.

Phillips in Association with Bacs & Russo

The Unicorn's existence was legendary and few people in the industry had even known about it until it was revealed in 2013 that famed collector John Goldberger had acquired the watch. "The world's jaw collectively dropped when they knew, … and we are absolutely thrilled to have the opportunity to auction it," said Boutros. Phillips hopes to sell the timepiece for more than $3 million when it hits the auction block Saturday in Geneva.

John Goldberger