Independent Senator Lidia Thorpe has interrupted King Charles' visit to Parliament House, calling out during proceedings in the Great Hall immediately after he finished his speech.
The Victorian senator, a Gunnai, Gunditjmara and Djab Wurrung woman, was heard shouting "give us our land back", "not your land" and "you are not my king. You are not our king".
She also called for the king to "give us a treaty", and was heard saying "f— the colony".
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She was escorted out of the room by security.
Earlier, Thorpe had called for Australia to become a republic on the back of a treaty with Indigenous peoples.
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"There's unfinished business that we need to resolve before this country can become a republic. This must happen through treaty," she said.
"We can move towards a treaty republic now. The two processes are not opposed, they're complimentary.
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"As First Peoples, we never ceded our sovereignty over this land. The Crown invaded this country, has not sought treaty with First Peoples, and committed a genocide of our people. King Charles is not the legitimate sovereign of these lands.
"Any move towards a republic must not continue this injustice. Treaty must play a central role in establishing an independent nation."
Thorpe appeared to be involved in a scuffle with a police officer outside the Australian War Memorial during Charles' visit, and was also pictured turning her back while waiting for the monarch when God Save The King was played at Parliament House.
Thorpe's anti-colonial and anti-monarchical views have been well-known for some time.
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She made global headlines in 2022 after the last federal election when she tried to change her oath of allegiance while being sworn into the Senate.
"I sovereign, Lidia Thorpe, do solemnly and sincerely swear that I will be faithful and I bear true allegiance to the colonising Her Majesty Queen Elizabeth II," she said with her fist raised in the air.
"Colonising" is not in the formal oath, and she was required to recite the exact words provided to her.