The ex-assistant to famed abstract expressionist Jasper Johns was sentenced to 18 months in prison Thursday for swindling the artist.

James Meyer, of Salisbury, Conn., stole 22 paintings from Johns and sold them out of a Lower Manhattan studio for a profit of $4 million between 2006 and 2011.

"I destroyed the close relationship that I had with the man who was my mentor, employer and friend since I was 21 years old," Meyer said. "I took for granted and betrayed someone who will forever have great meaning in my life."

Manhattan Federal Court Judge J. Paul Oetken ordered Meyer to pay $13.4 million in restitution to the artist and buyers of the unauthorized artworks. Not all of the paintings sold by Meyer are accounted for.