According to the Miami Herald:
The makers of Duff in South America say they aren’t allowed to talk to the U.S. media. Duff Mexico… would not respond to interview requests. And 20th Century Fox, which owns the rights to The Simpsons, said it would not comment on the story and would not say if it has a licensing agreement with any of the Duff producers.
(Source: blogs.laweekly.com)
