  We present an approach to monitor and control the strength of the
hybridization between electronic states of graphene and metal surfaces.
Inspecting the distribution of the $\pi$ band in a high-quality graphene layer
synthesized on Ni(111) by angle-resolved photoemission, we observe a new "kink"
feature which indicates a strong hybridization between $\pi$ and \textit{d}
states of graphene and nickel, respectively. Upon deposition and gradual
intercalation of potassium atoms into the graphene/Ni(111) interface, the
"kink" feature becomes less pronounced pointing at potassium mediated
attenuation of the interaction between the graphene and the substrate.
