ABC News global affairs anchor Christine Amanpour on Sunday threw cold water on one of her colleagues, Brian Ross, who had reported that Iran could have a functional nuclear weapon in as little as four weeks.

During a panel discussion on ABC, host Jake Tapper asked Ross how quickly Iran could build a nuclear device.

"Four to six weeks away, if they made the decision to do it," Ross claimed. "That’s some of the intelligence. They haven’t made that decision, that’s the key."

"That is so vastly disparate," Amanpour pointed out. "Other's say it could be a year. So, this is a guessing game that's gone on for years."

"It could be two years," ABC Senior Foreign Affairs correspondent Martha Raddatz agreed.

"That's the latest claim," Ross argued.

While Ross has won awards and broken many major stories during his tenure at ABC News, he is also renowned for making some of the biggest and most embarrassing mistakes in mainstream journalism.

In 2001, ABC's senior investigative reporter falsely claimed that Iraq and Saddam Hussein were behind anthrax attacks in the U.S. He reported in 2009 that Ft. Hood shooter Nidal Malik Hasan had made an "attempt to reach out to al Qaeda." Gawker found that Ross had edited footage in 2010 to make spontaneous acceleration in Toyota cars appear worse than it actually was.

Most recently, Ross was blasted by conservatives when he wrongly reported that Jim Holmes -- the 24-year-old accused of a shooting rampage at a theater in Aurora, Colorado -- had been associated with the tea party.

"Brian Ross is responsible for several of the establishment media’s most shameful and reckless journalistic falsehoods of the last decade," The Guardian's Glenn Greenwald told Politico. “His reporting philosophy seems to be to go on TV and say whatever he thinks will garner attention and create ‘scoops,’ without the slightest concern for whether it’s actually true.”

Watch this video from ABC's This Week via Think Progress, broadcast Sept. 16, 2012.