"Lifeless," "ghastly" and "disappointing" were also adjectives thrown out to describe the work by Paul Emsley, an award-winning artist who painted Middleton, 31, against his trademark black background with a slight smile, or smirk, and lines visible around her face.
Now Emsley, who said at the time he wanted to capture Middleton's natural beauty, is fighting back against the harsh critiques that caused the portrait to become an online sensation, for all the wrong reasons.
"At first the attacks were so vicious that there was a point where I myself doubted that the portrait of the duchess was any good," Emsley, 75, told Hello magazine. "But now I've had time to reflect, I am still happy with it and am getting on with my life. There is nothing I would have changed."
After devoting nearly four months of his life to the painting, Emsley says the criticisms that he describes as a "witch hunt" and a "circus" were "destructive" to him and his wife and two daughters.
"Some of the words written about it were so personal. I'd be inhuman if I said it didn't affect me," he said. "When you take on commissions like this it is hazardous and you expect a bit of flak, but I expected nothing like the criticism I have received. I didn't expect it to go to the levels it did."
"It really wasn't pleasant and I stopped reading what had been written," Emsley said of the conversation that exploded online and in the worldwide press. "I have coped with the criticism by going back into my studio and getting on with it."
Emsley was on hand at the National Portrait Gallery in London Jan. 11 as Middleton, whom helped select Emsley as the artist, and her husband, Prince William, saw the portrait unveiled for the first time.
Middleton, who sat for the portrait in May and again in June, reportedly described the work as "amazing" and "brilliant," while William called it "beautiful."
Emsley now says that if everyone could see the portrait in person, they too would agree with the royals.
"I believe half the problem is the portrait doesn't photograph well and I would encourage people to go and see it [at the National Portrait Gallery]," he told Hello.
He also had high praise for his subject, Middleton, who made a rare public appearance to see the portrait after her hospitalization in December for hyperemesis gravidarum, severe morning sickness associated with her first pregnancy.
"She struck me as enormously open and generous and a very warm person," Emsley said. "After initially feeling it was going to be an unsmiling portrait I think it was the right choice in the end to have her smiling. That is really who she is."