An online article claiming Lindiwe Sisulu cried upon learning she would no longer be defence minister was a "fabrication", her spokesperson said on Thursday.
In an open letter to Mail&Guardian editor Nic Dawes, Ndivhuwo Mabaya said the incident "only happened in your journalist's imagination".
Dawes said the newspaper stood by the story.
The story, which appeared on the Mail&Guardian website, was based on information from an unnamed senior ANC and government official.
The source claimed Sisulu saw her new portfolio as public service minister as less prestigious and therefore as an effective demotion.
The official is quoted as saying: "What angered her even more was that she was told about the decision to remove her only this morning [Tuesday], hours before the announcement."
Mabaya said the story was "fiction, fabrication, untrue, written to be sensational, and malicious".
He said Sisulu welcomed the challenge of a new portfolio and saw it as an opportunity to improve the lives of South Africans.
Furthermore, Sisulu had "known for some time" about President Jacob Zuma's plans to move her to a new portfolio and was alone in her office when she was informed of it.
"It is sad and says a lot about the level of journalism when a senior journalist like Matuma Letsoalo can stoop so low [as] to believe this kind of fiction and fabrication."
In Zuma's Cabinet reshuffle on Tuesday, Sisulu was deployed to take over the portfolio of Roy Padayachie, who died last month.
Sisulu was succeeded by the previous Correctional Services Minister, Nosiviwe Mapisa-Nqakula.