A fruitful combination of absorption and gated luminescence spectrophotometry allowed us to gain insight into the proton-assisted dissociation of a triple-stranded dinuclear europium helicate in water. This process involves a key dimetallic double-stranded complex Eu2L2 as already observed in the self-assembly process of the triple helicate. The slow unravelling of the first strand, which is triggered by the protonation of its two carboxylate groups, dominates the whole disentangling mechanism of the supramolecular edifice. The solvolytic dissociation in water is rather slow (kD = 4(1) × 10−4 s−1) and is catalysed by H+ ions (k = 0.12(3) M−1 s−1). These lanthanide helicates, which are characterised by high kinetic inertness over a wide range of pH and high thermodynamic stability in water, are promising building blocks for the development of novel fluorescent biomarkers.