Urban Skyscraper Billboard Mockup

Generate a hyper-realistic image of a large blank billboard mockup on the side of a sleek, modern skyscraper with a glass and steel facade, set against a clear blue sky with wispy clouds, with the billboard appearing to be slightly curled at the top right corner, and a subtle shadow cast on the building's surface, with a secondary skyscraper visible in the background to the left, and a faint watermark pattern of 'FREEPiK' repeated diagonally across the image, with realistic lighting, natural shadows, and detailed textures, as if shot for a high-end design editorial or campaign photograph.