On Tuesday morning, the Democratic Alliance (DA) officially rescinded Patricia de Lille's membership from the party.
The party's top decision-making body, the federal executive, made the announcement, briefly outlining the history of the battle between De Lille and the party's national leadership.
De Lille faces accusations by the DA of multiple allegations, including misconduct.
Shortly after the briefing, Natasha Mazzone spoke on Radio 702's Eusebius McKaiser Show, saying that it's against the party's constitution if a DA member expresses the intention to resign.
The DA cited clause 220.127.116.11 in its constitution, that says if a member publicly declares his or her intention to resign, then their membership ceases immediately.
"The Democratic Alliance constitution provides that a member ceases to be a member when he or she publicly declares his or her intention to resign and or publicly declares his or her resignation from the party. Now it's ironic that I talk to you, as it was on your show that Mayor De Lille indicated and made known her intention to resign from the Democratic Alliance."
James Selfe, the DA's federal executive chairperson, made the announcement at a media briefing in Cape Town.
In February, the embattled mayor survived a motion of no confidence but the party voted to recall her as mayor in an internal motion of no confidence against her in April.
It was an interview on the Eusebius Mckaiser Show recently that sealed her fate after weeks of confusion and public spats between Cape Town's mayor and the party's leadership.
In it, she told McKaiser that she would walk away from the DA, saying the writing was on the wall.
De Lille must now either resign as mayor or take the matter to court.
Deputy Mayor Ian Neilson will take over as acting mayor immediately and a new mayor would be elected "as soon as possible". The council now has 14 days to elect a new mayor, according to the Municipal Structures Act.
For its part, the DA leadership has acknowledged the damage that the conflict and confusion has caused, formally apologising to Cape Town ratepayers.
De Lille, meanwhile, announced she will address the media later today.