De Ruyter had resigned in December, saying a lack of political support had made his position "untenable", and served his notice period until the end of March.
However, following an interview on Tuesday with eNCA in which he criticised the ANC, Eskom's board of directors called De Ruyter to a meeting on Wednesday, after which they announced that he would be leaving immediately.
In a statement on Thursday, government said executives at state-owned corporations should raise grievances through "formal channels".
"Government also noted public comments on social media and that De Ruyter's exit from Eskom is linked to an interview that he had earlier this week," it said, without denying or confirming if his exit was linked to the interview.
In the interview with eNCA, De Ruyter said the corruption at Eskom was like a cancer which "has just metastasised and grown over the body of the whole organisation".
Asked by the interviewer whether Eskom was a "feeding trough" for the ruling party, De Ruyter said "the evidence suggests that it is", but did not provide any evidence.
De Ruyter, who took up the top job at the utility three years ago, also alluded to a senior politician in the ruling ANC who was aware of the corruption without providing names.
De Ruyter could not be reached for comment.
ANC party secretary-general Fikile Mbalula rejected De Ruyter's corruption claims and said he was "a failure" as CEO for his inability to revamp Eskom.
"The ANC does not support corruption. The ANC is not corrupt," he told a news conference.
Separately, ANC spokesperson Mahlengi Bhengu-Motsiri told Reuters that De Ruyter should, as required by law, have reported the crime he alleges.
"If not he will himself be eligible for arrest due to unlawful concealment of a crime," Bhengu-Motsiri said.
The DA, however, has lodged a legal application requesting Eskom's management to publicise the name of the "high-level politician" De Ruyter alluded to have been involved in corruption.
Khaya Magaxa, the chairperson of Parliament's Portfolio Committee on Public Enterprises, said the committee has a constitutional responsibility of oversight over Eskom and "we can’t ignore those serious allegations".
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