In situ detection of hypochlorous acid (HOCl) is critical for understanding its complex physiological and pathological roles. Fluorescent probes, known for their sensitivity and selectivity, are the preferred approach for such detections. Anthracene carboxyimide, an analog of naphthalimide, offers extended excitation and emission wavelengths, making it an excellent candidate for developing new fluorescent probes that address the limitations of naphthalimide. In this study, we designed a novel HOCl-specific fluorescent probe, AC-Se, by incorporating highly reactive selenium into anthracene carboxyimide. The probe exhibits a 104-fold fluorescence enhancement, a large Stokes shift of 72 nm, and a low detection limit of 36.2 nM. Moreover, AC-Se responds rapidly to HOCl within 4 seconds, enabling real-time intracellular monitoring of both exogenous and endogenous HOCl.