Last week, Leonardo da Vinci's "Salvator Mundi" became the most expensive work of art ever sold, going for $450 million at Christie's.

Auctioned off to an unknown buyer on the phone after a protracted, 19 minute bidding war, the masterpiece's road to fetching nearly half a billion dollars actually began in 1958 — when it originally sold for less than $200, an art dealer who once owned the piece told CNBC.

After the 1950's, "Salvator Mundi's" trail went cold until around 2005, when art dealers Alex Parish and Robert Simon bought it an estate sale in New Orleans for $10,000.

At the time, Simon, who runs Robert Simon Fine Arts on the Upper East Side of Manhattan, thought the painting was a diamond in the rough. That said, he had no inkling it was an actual da Vinci.

"It appeared to be a damaged, but worthy Renaissance-era work," Simon told CNBC last week.

"I thought it was beautiful but battered, and greatly overpainted. In my wildest imagination I would never have thought it was a da Vinci," he added. "Perhaps, if we were very, very lucky, it would be attributable to one of his peers."

Simon and Parish enlisted noted New York University paintings conservator Dianne Dwyer Modestini to work on the restoration. A few years into a laborious process, Simon had a moment of revelation.

"Once the layer ancient paint were scraped down and the original work started to emerge, this magical feeling took hold. I knew this was the real deal" Simon exclaimed. "Seconds later, those thoughts turned to fear! I mean, now I have a bona fide da Vinci on my hands, how the heck do I keep it safe?"