This letter alleviates the existing lacuna about the true source of cross-polarized (XP) fields in an equilateral triangular microstrip patch. No information about its sources is available so far. Following the existing knowledge about rectangular or circular microstrips, we have extensively examined the dominant and the first two higher-order modes. The theoretical analysis indicates that each of them is with equally probable modal patch currents causing the XP radiations. To identify the actual contributing mode(s) or discriminate the insignificant ones, an intuitive mild perturbation has been employed as a tool. This investigation eventually identifies that it is neither a higher mode nor any specific orthogonally polarized resonance. This finally establishes the primary radiating mode itself as the most significant source of the XP fields which is experimentally verified using a C -band prototype.