In this work, we address a mechanistic issue on AIE process and correct a long-held misconception on stilbene photoluminescence. E–Z isomerisation has been generally recognized as the cause of emission quenching in stilbene solutions. A natural question arisen from this common belief is whether suppression of E–Z isomerisation by aggregate formation in a stilbenic fluorogen system is responsible for its AIE phenomenon. Monitoring of the structural change of a stilbene derivative named 1,2-diphenyl-1,2-di(p-tolyl)ethene by NMR during UV irradiation reveals that the E–Z isomerisation is not involved in its AIE process under the normal photoluminescence spectral measurement conditions.