In this context, we have recently observed the solid solutions CeMn1-xCdxPt (x = 0 and 0.15) with trivalent Ce 3+ , adopting the hexagonal ZrNiAl type, meaning isostructural with the pristine CeCdPt and CeMnPt structures. In addition, the analogue solid solution YbCdxMn1-xPt (x = 0.13) with divalent Yb 2+ was characterized in the rival orthorhombic TiNiSi type structure, while the hypothetical endmembers "YbMnPt" and "YbCdPt" have remained elusive. Despite the differences in atomic sizes and electronic configurations between Mn(d 5 ) and Cd(d 10 ), the two metals randomly mixed at one crystallographic site in both Ce and Yb based systems, which are therefore considered to be quasi-ternary derivatives of the previously vacant RE-Mn-Pt systems. We expanded our investigations to the Eu-Mn-Pt system, under speculations that the imaginary ternary equiatomic "EuMnPt" may be isostructural to the isovalent EuCdPt and EuMgPt which are both reported in the TiNiSi type structure. 9-10 However, the targeted synthesis of the "EuMnPt" phase was unsuccessful. Therefore, similar partial Mn for Cd isovalent substitutions were conducted to prepare the solid solution EuCd1-xMnxPt and, to our surprise, an unexpected Cd/Mn strong differential site preference, not observed in Ce and Yb analogues, results in a genuine quaternary phase Eu2Mn1-xCd1+xPt2 (x = 0.11), with the orthorhombic LaNiAl type structure, as indicated by single crystal X-ray diffraction data.