Most of the negative group delay (NGD) circuit recent investigation were focused on the classes of lowpass and bandpass categories. Few research works are currently available in the literature on the typical high-pass (HP) NGD function. This paper introduces an original HP-NGD circuit theory of four-port passive topology constituted by a single lumped capacitor. The S-matrix equivalent model of the innovative topology is established from the admittance matrix. Then, the basic frequency analytical responses are expressed. Then, the GD model is derived in function of the capacitor. It was found analytically that the four-port mono-capacitor passive circuit is susceptible to behave originally as an unfamiliar HP-NGD function. An innovative HP-NGD analysis is explored in addition to the expression of synthesis design equation in function of the expected NGD cutoff frequency which is linked to NGD optimal value. The validity of the established HP-NGD circuit theory is verified with a proof of concept (POC). As expected, the HP-NGD behavior showing a good correlation between analytical model and simulation is obtained.