Cysteine plays a crucial role in cellular functions and in human pathologies. However, the development of cysteine probes with extremely accurate detection is still a key challenge for the field. Herein, we have fully characterized and developed a novel selective fluorescent probe: red emission, aqueous detection and large Stokes' shift for cysteine (Reals-C). Key in the probe synthesis is a Michael addition onto an acroylate group and subsequent intramolecular cyclization. The probe exhibits analyte detection via an intricate role set up by the leaving groups so to discriminate and form the red-emissive analyte sensing platform (lambda(ex) = 471 nm, lambda(em) = 637 nm) through a chemical cascade pathway. Furthermore, the sensing ability of the probe was demonstrated by both in vitro and in vivo assays. This probe enables for successfully endogenous cysteine sensing in HaCaT human keratinocytes through comparison with a commercial thiol-sensitive probe; Reals-C shows excellent in vivo cysteine detection in a drug-induced animal liver injury model.