Jasper Johns’ former assistant has been sentenced to 18 months in jail after admitting he stole artworks from the artist’s studio.

James Meyer, 53, confessed to stealing 22 unfinished pieces and selling them to a New York gallery.

“I am truly devastated that I destroyed the close relationship that I had with the man who was my mentor, employer and friend,” he said in court in New York.

James Meyer was ordered to pay restitution of $13.5 million to Jasper Johns and others.

Jasper Johns, 84, is best known for sculptures and paintings of the American flag, including one that sold at auction last year for a record $36 million.

James Meyer was an assistant in Jasper Johns’ Connecticut studio for 25 years, from the age of 21.

In August 2014, James Meyer pleaded guilty to one count of interstate transportation of stolen property and admitted moving artworks from the studio to an art gallery in Manhattan between 2006 and 2012.

“I took for granted and betrayed someone who will forever have great meaning in my life. For that, I have profound remorse,” James Meyer told the courtroom.

Jasper Johns had asked James Meyer to destroy some of the works, and had not given any authorization for them to be sold.

James Meyer – who arranged to have around 40 pieces sold through a New York gallery – told the unidentified gallery owner the incomplete works had been personal gifts from Jasper Johns, and provided fake documentation.

He also created fake inventory numbers and pages in a ledger book of registered Jasper Johns artwork to further assure the gallery owner the works were authorized.

James Meyer received approximately $4 million from the sale of the artworks by the gallery. In court on April 23, James Meyer was ordered to forfeit the amount he made from the sales, as well as paying the $13.5 million to compensate the artist and four unidentified buyers.

Prosecutors said one buyer who agreed to return the artworks to Jasper Johns had spent over $7 million on them.

After his arrest in August 2013, James Meyer cooperated with the government and helped recover stolen works from the buyers, prosecutors said. He also turned over 41 additional works that investigators did not know about.