In a grid-forming (GFM) modular multilevel converter-based high-voltage direct-current (MMC-HVDC) system, one terminal operates under dc-link voltage control, while the other operates under active power control. This paper analyses the inertia response of the dc-link voltage-regulated MMC. It is found that when frequency disturbances occur in the dc-link voltage-regulated MMC-connected grid, the remote ac grid can provide inertia support through dc-link voltage-to-active power droop control. However, this paper reveals that, although remote grid energy can be utilized for inertia support, inertia provision capability is constrained by dc-link voltage and dc-link current limitations. In addition, this study quantifies the inertia provision capability boundary within those limitations. Simulation results validate the accuracy of the derived boundary.