A major German newsmagazine has fired an award-winning journalist after he admitted to fabricating sources in at least a dozen articles since 2011.

Der Spiegel said on Wednesday that reporter and editor Claas Relotius “falsified his articles on a grand scale and even invented characters, deceiving both readers and his colleagues.”

“This has been uncovered as a result of tips, internal research and, ultimately, a comprehensive confession by the editor himself,” Der Spiegel said in a statement on its website.

Relotius has been honored with several prestigious awards in recent years, including CNN’s Journalist of the Year in 2014 and the European Press Prize in 2017. He appeared on Forbes’ list of “30 Under 30” for European media last year.

Several major features nominated or winning awards are among the articles in question, including “Number 440,” about prisoners at Guantanamo Bay that was named Deutscher Reporterpreis story of the year in 2016.

Relotius admitted at least 14 of nearly 60 articles he has written for Der Spiegel were at least partially fabricated. Der Spiegel said it would continue to investigate and report publicly on the findings.

It’s unclear whether Relotius fabricated stories for other major German outlets that published his work, including Cicero and the Financial Times Deutschland.

“I’m so angry, horrified, shocked, stunned,” Der Spiegel deputy foreign editor Mathieu von Rohr tweeted Wednesday. “Claas Relotius faked, he cheated on us all.”

Relotius authored “Where they pray for Trump on Sundays,” a 2017 Der Spiegel feature that purportedly examined the president’s supporters in the rural Minnesota town of Fergus Falls.

Two Fergus Falls residents accused Relotius of several falsehoods in the story, including lying about the town’s welcome sign, in a piece they published on Medium on Wednesday.

“Not only did Relotius’ ‘exposé’ on Fergus Falls make unrecognizable movie-like characters out of the people in my town that I interact with on a daily basis,” Michele Anderson and Jake Krohn wrote, “but its very basic lack of truth and its bizarrely bleak portrayal of the place I love left a very sick, unsettled feeling in the pit of my stomach.”

Revelations of journalists making up sources and facts ― a cardinal sin in the profession ― have plagued major publications. In November, the Houston Chronicle retracted eight stories after an investigation determined a former reporter invented sources and quotes.

This article has been updated to include Anderson and Krohn’s article on Medium.

CORRECTION: A previous version of this story mischaracterized Anderson and Krohn as a couple.