The 20-year hunt for a stolen Picasso painting was found by an Amsterdam art detective

What would be your reaction if two men knocked on your door and handed you one of the most amazing paintings of Spanish artist Pablo Picasso?

This bizarre — though beautiful — moment happened to the respected Dutch art detective, Arthur Brand earlier this month and therefore resolving a 20-year-old grand larceny cold case.

"When I unwrapped the painting, I was speechless. Colors of Picasso were astonishing me." Brand told to ABC News, describing one of the most important moments of his professional life.

In 1980, Sheikh Abdul Mohsen Abdulmalik Al-Sheikh purchased Picasso's "Buste de Femme" for $4.5 million. The Saudi Prince kept the 1938 masterpiece of Picasso's muse under lock and key aboard his $50 million yacht in the Antibes — an exclusive resort on the French Riviera — until March 11, 1999 when it was stolen.

Despite the $450,000 reward Al-Sheikh offered for its return, the painting was never recovered until 20 years later due to the work of Brand.

Brand, 48, began his career in 2002 and started building a network of informants, collectors, police, and international criminals. The veteran detective was close to former international smuggler Michel van Rijn, who has since collaborated with the police as an informant.

Brand gained notary as an art detective after negotiating with two different criminal organizations to secure the return of a Salvador Dali surrealist painting called Adolescence (1941) and Tamara de Lempicka's La Musicienne (1929). The two paintings were stolen from a Dutch museum by a masked gang in 2009.

A collector himself, Brand said that 30 percent of art pieces sold are fake.

As for "Buste de Femme," the masterpiece was a part of the private collection of Picasso and hung inside his house in France until his death in 1971.

"Only few pictures of this painting existed and it was before the era of Internet," said Brand, who found out about the painting's theft in 2015.

"I made few phone calls to my sources to let them know I would like to help returning the painting to the legal market.

Last week, Brand received a phone call from the alleged owners of the painting. Two men showed up to Brand's house in Amsterdam, Netherlands, with the $28 million-valued Picasso wrapped in garbage bags, he said.

Within the same week, experts from the New York-based Pace Gallery flew to Amsterdam to authenticate the masterpiece. Insurance will decide the possible conditions of returning the painting to the Al-Sheikh.

In possession of the painting for one night, Brand, could not resist and hanging it on his own wall, he said.

Looking at the painting while smoking a cigarette on his balcony for few hours, Brand's house became the most expensive in Amsterdam as he admitted to ABC News.