In this work we introduce the concept of natural ageing via precipitation arising from eutectic cell structure (PEC-ageing). Natural age-strengthening in grey cast iron at room temperature is long recognised yet still poorly understood, despite its beneficial effect on tensile strength and machinability. We investigate its un derlying mechanisms by comparing fresh and naturally aged industrial grey cast iron using high-resolution synchrotron Wide-Angle X-ray Scattering (WAXS), complemented by scanning electron microscopy and X-ray energy-dispersive spectroscopy. A strict sample-preparation process was designed to minimize artificial ageing and X-ray attenuation artefacts. We present direct experimental evidence of an X-ray diffraction peak that forms upon natural ageing in grey cast iron. Based on its position in reciprocal space, a plausible candidate for this peak is the iron nitride phase Fe4N. Spatially resolved analysis further shows that this phase is strongly localised along eutectic cell boundaries, supporting a nitride-related, boundary-mediated precipitation mechanism (PEC-ageing) as the main driver of the ageing phenomenon. These results provide a spatially resolved description of natural ageing in grey cast iron, establish WAXS as a powerful tool to track ageing-related changes in the bulk, and highlight that logistics and sample preparation remain the main practical challenges for future in-situ studies.