South Africa's highest court has ruled that the public protector - the state official in charge of investigating corruption - had lied under oath and acted in bad faith.
The devastating judgement will add weight to claims that Busisiwe Mkwebane is involved in a dirty-tricks campaign to undermine President Cyril Ramaphosa and halt his campaign against high-level corruption, says the BBC's Andrew Harding in Johannesburg.
Last week, Ms Mkwebane ruled that Mr Ramaphosa had misled Parliament and should be investigated.
Her critics say she is being used by supporters of former President Jacob Zuma, who is fighting corruption allegations himself.
Ms Mkwebane says her work is being done according to the law and the constitution.
Many of Ms Mkhwebane's recent reports have become swamped by scandal and led to claims that she is siding with Mr Zuma's faction within the governing African National Congress (ANC), our reporter says.
Mr Ramaphosa replaced Mr Zuma as party leader last year after the then-president had become embroiled in numerous corruption scandals.
The President said on Sunday that he would be mounting a legal challenge against the public protector's report that concluded he had deliberately misled parliament over a campaign donation for May's election.
He denied the allegations, saying the report was "fundamentally and irretrievably flawed".
The courts have overruled Ms Mkhwebane on several occasions recently.
In the latest ruling, the Constitutional Court fined Ms Mkwebane £50,000 ($62,000) in legal fees from her own pocket in a dispute between her office and South Africa's Reserve Bank.
Ms Mkhwebane has previously denied any wrongdoing.
Reacting to the judgement on Monday, she noted that the court had not been unanimous, our reporter says.
Ms Mkwebane was backed for the public protector's job by an overwhelming 263 MPs during a debate in the 400-member Parliament.
She has only been in the job for less than three years but has already faced two attempts for her removal from office, accusations of political bias, and the most scathing of all, a reprimand from the constitutional court.
Another accusation that she is a spy and a loyalist of former President Zuma, are not dissimilar to those levelled against her predecessor, Thuli Madonsela, who was accused by allies of Mr Zuma of working for US spy agency CIA.
These claims have not been substantiated.
Ms Mkwebane is not one to shy away from a fight, she is also not one to accept defeat, not even from the highest court, it seems.
She is determined to clear her name and hopefully restore the public's faith in her as their protector.