In today's digital era, the rapid spread of fake news undermines both social unity and democratic institutions, demanding effective countermeasures. Current browser extensions to counter fake news have significant limitations, such as opaque models, dependency on traditional Machine Learning (ML) techniques, lack of explanatory features, and limited focus on detection without user engagement support. This paper introduces Aletheia, a novel browser extension that addresses these shortcomings by leveraging Retrieval Augmented Generation (RAG) and Large Language Models (LLMs) to enhance fake news detection and provide evidence-based explanations. Additionally, Aletheia incorporates two key components: a Discussion Hub, enabling users to discuss instances of fake news, and a Stay Informed feature, which displays the latest fact-checks. Aletheia surpasses state-of-the-art methods according to experimental results.