Nanoscale control over the second-order photon correlation function ${g}^{(2)}(\ensuremath{\tau})$ is critical to emerging research in nonlinear nanophotonics and integrated quantum information science. Here we report on quasiparticle control of photon bunching with
g(2)(0)>45 in the cathodoluminescence of nanodiamond nitrogen vacancy (
NV0) centers excited by a converged electron beam in an aberration-corrected scanning transmission electron microscope. Plasmon-mediated
NV0 cathodoluminescence exhibits a 16-fold increase in luminescence intensity correlated with a threefold reduction in photon bunching compared with that of uncoupled
NV0 centers. This effect is ascribed to the excitation of single temporally uncorrelated
NV0 centers by single surface plasmon polaritons. Spectrally resolved Hanbury Brown--Twiss interferometry is employed to demonstrate that the bunching is mediated by the
NV0 phonon sidebands, while no observable bunching is detected at the zero-phonon line. The data are consistent with fast phonon-mediated recombination dynamics, a conclusion substantiated by agreement between Bayesian regression and Monte Carlo models of superthermal
NV0 luminescence.