Carl C. Icahn has long maintained that he never has had a “formal” position within the Trump administration. But he resigned from his advisory role all the same.

“Today, with President Trump’s blessing, I ceased to act as special advisor to the President on issues to regulatory reform,” Mr. Icahn posted to Twitter, linking to a copy of his Aug. 18 resignation letter.

But the tweet came shortly before The New Yorker posted an article on Friday about the conflicts created by Mr. Icahn’s advisory role. The article’s author, Patrick Radden Keefe, said that the White House had told him that Mr. Icahn had been fired on Aug. 14.

So ends one of the more closely scrutinized relationships between President Trump and one of his fellow business moguls. Mr. Icahn owns a big stake in the oil refiner CVR Energy, and the financier has pressed for changes to regulations that require refiners to mix ethanol into gasoline.