The 18-year-old Swedish climate activist has suggested organisers of COP26 may have been "too scared" to invite her to the summit.
Speaking to the BBC, Greta Thunberg told Andrew Marr that she had not been "officially" invited to the event, despite being one of the world's most well-known climate change activists.
“I don’t know. It’s very unclear. Not officially [invited]," she said. “I think that many people might be scared that if they invite too many radical young people, then that might make them look bad.”
Elsewhere, with respect to representation, she criticised the climate change conference for what she saw as not ensuring enough delegates from developing countries were invited.
"We need more representation from the so-called Global South, from the most affected people and areas," she said.
“It’s not fair when, for example, one country sends lots and lots of delegates and then another country is very under-represented," she added.
“As long as we keep ignoring the historical responsibility of the countries of the Global North and as long as we continue to ignore it, the negotiations will not have a successful outcome."
On Friday, Thunberg has joined activists in London to chant “we are unstoppable, another world is possible” ahead of the COP26 summit.
Environmental campaigners are lobbying against the global finance system investing money in the use of fossil fuels.
Congregating outside the Standard Chartered headquarters in central London, protesters chanted: “What do we want? Climate justice. When do we want it? Now.”
Earlier, demonstrators chanted “Ensure our future, not pollution” as they made their way from Lloyd’s of London to Macquarie Capital.
Around 70 campaigners were in at Friday morning’s protests, with numbers growing at each site.
The protests come after campaigners revealed a whopping £2.7trn investment in fossil fuel extractions since the Paris Agreement in 2015, where world leaders - for the first time - signed legally binding documents pledging to keep global warming below 2C with a 1.5C target, and to hit net zero by the middle of the century.
Thunberg is due to head north to Glasgow afterwards, where COP26 will convene with world leaders and representatives from nearly 200 countries, including US president Joe Biden.
As the leader of the host country, Boris Johnson has called on the world to "grow up" in the run up to the summit, today describing the conference as "[not] a chance we can miss" to save the planet.
However, days ago, his government came under scrutiny after slashing flight duty on heavily polluting domestic flights.
While Thunberg is set to attend the summit, she has expressed some pessimism about the event previously - saying she think it's unlikely it will achieve "big changes".
How successful the conference will be was thrown into question when it emerged that Vladimir Putin, president of Russia, one of the world's biggest polluters, would not be attending.
Xi Jinping, president of China and the world's biggest polluter, will attend via video link.
Politicians, journalists, activists and experts will be among the some 25,000 people that will attend COP26 this weekend, which runs from Sunday 31 October 2021 to Friday 12 November.