The rapid integration of generative artificial intelligence (GenAI) into marketing communication is changing how brands create advertising content. This study investigates how AI disclosure in advertising influences consumers’ attitudes toward the advertisement (Aad), perceived brand authenticity (BA), and purchase intention (PI). It explores the moderating effect of AI aversion and brand trust (BT). The growing integration of AI-generated content (AIGC) in marketing and regulatory requirements for disclosure under the EU AI act motivates this research. It addresses the lack of empirical evidence on consumer responses to AI transparency. A between-subject online experiment exposed female participants familiar with the fashion brand Mango to either an AI-disclosed or non-disclosed AI-generated advertisement. Established measurement scales captured Aad, BA, PI AI aversion, and BT. Data was analysed using regression analysis and moderation models. Results showed no significant direct effect of AI disclosure on Aad or BA, which contradicted the AI-authorship effect documented in prior studies. However, BA and Aad significantly predicted PI, BA showing a stronger influence. Neither AI aversion nor BT significantly moderated the relationship between disclosure and consumer responses, although BT strongly correlated with PI. It was revealed through exploratory qualitative insights that while most respondents remained indifferent to disclosure, a minority expressed concerns about authenticity, creativity, and ethics. Findings suggest that mandatory AI disclosure might not harm consumer perceptions, but authenticity remains critical for driving purchase intentions. To sustain trust and authenticity in AI campaigns, marketers should frame AI as a creative enhancer rather than a human replacement.