The direct synthesis of graphene on dielectric substrates has attracted growing interest due to its potential for scalable, transfer-free integration in electronic and photonic applications. However, graphene grown on dielectrics typically exhibits lower carrier mobility compared to copper-grown counterparts, limiting its performance. Here, we report the synthesis of large-area graphene on Al-rich reconstructed c-plane sapphire (0001) via chemical vapor deposition (CVD) and reveal that, over time and under ambient storage conditions, a spontaneous decoupling occurs at the graphene–sapphire interface. Raman spectroscopy reveals a reduction in both strain and doping in the aged samples, consistent with electrical transport measurements showing a twofold increase in carrier mobility. X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (cross-sectional TEM) identify the intercalation of oxygen-containing species at the interface as the mechanism responsible for the decoupling. These findings uncover a previously unrecognized pathway to enhance the electronic performance of directly grown graphene on sapphire, reinforcing the viability of this platform for future scalable graphene-based technologies.