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| - In mid-March 2026, a rumor circulated online that Swedish activist Greta Thunberg had been diagnosed with stage IV glioblastoma, an aggressive form of brain cancer.
For example, on March 13, a Facebook post (archived) read:
BREAKING NEWS: Greta Thunberg is reportedly facing a major trial in her life after doctors discovered she has stage IV Glioblastoma, a very aggressive form of brain cancer.
The news has deeply worried many people around the world who have followed her activism and voice for climate awareness. Many are sending prayers, positive thoughts, and messages of support, hoping she will have the strength, healing, and peace needed during this incredibly difficult time.
Please join in sending love, encouragement, and support to Greta Thunberg. May light, hope, and compassion surround her throughout this challenging journey.
The post included an image purportedly showing Thunberg sitting upright in a hospital bed. Text in the graphic read:
A message for all supporters of Greta Thunberg: Our beloved climate activist is now facing one of the greatest trials of her life as she confronts a serious illness. Her family and close supporters ask for your prayers, love, and encouragement during this difficult time.
Versions of the rumor spread primarily on Facebook and Snopes readers contacted us to ask whether the claim was true.
We first used search engines such as Bing, DuckDuckGo and Yahoo to locate possible evidence from credible sources about the Swedish activist having stage IV glioblastoma. If the story were true, journalists with reputable news outlets, such as The Associated Press or Reuters, would have widely reported on it. That was not the case.
The rumor is fictional. It originated from the Facebook page Climate Wake Up (archived) and blog pages that use artificial intelligence tools to create inspiring or shocking stories about public figures. Therefore, we rated this claim false.
For instance, the image in the post about Thunberg supposedly having an aggressive form of brain cancer is a product of AI image-generation software. The image shows several signs of AI generation, including an unnaturally smooth facial appearance, slightly artificial-looking lighting and a polished, synthetic overall quality. In addition, Thunberg's appearance in the picture was not consistent with authentic footage posted on her verified social media accounts around the same time the rumor was spreading. In reality, the activist's hair is a different style, as of this writing, to what can be seen in the fake image.
Creators of such content capitalize on social media users' willingness to believe and share the made-up stories, profiting from advertising revenue on external websites to which the posts link. (Snopes has previously reported on the business strategy.)
We contacted a manager of the Climate Wake Up Facebook page to ask why it had created the false story without a disclaimer to note its inauthenticity. We will update this story if we receive a response.
Many posts spreading the false rumor about Thunberg's alleged cancer diagnosis include links in the comment sections to advertisement-filled articles hosted on WordPress blogs, rather than reputable news media outlets.
The article and the social media posts' captions show several indications that they feature AI-generated text. The wording is vague and emotionally loaded and it features generic background information rather than verifiable reporting. The text does not identify a hospital, doctor, spokesperson, family member or any other concrete source. GPTZero, a tool that aims to detect AI-generated writing, determined with 99% certainty that the article's text was AI-generated.
Moreover, the article employed an anti-crawling technique that involves visually substituting certain Latin letters with similar-looking characters from other alphabets. For instance, the Cyrillic letter "п" appeared in place of the Latin letter "n."
Other software that screens images for signs of AI, such as Sightengine and Hive Moderation, determined the in-question image was likely created with generative technology as well.
Let us note here: These types of AI detection tools are fallible. Snopes cautions people against using them for definitive answers on media's authenticity without supporting evidence.
The fictional story about Thunberg resembled glurge, which Dictionary.com defines as "stories, often sent by email, that are supposed to be true and uplifting, but which are often fabricated and sentimental."
For further reading, in March 2025, we traced the source of a false story, that spread via similar methods, about tech billionaire Elon Musk supposedly paying a sick child's medical bills.
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