Peter’s confession is presented with a varying text in each of the Synoptics. Absent in Mark 8:29, sonship language is expressly used in Matthew 16:16. English versions provide a literal but awkward translation of Luke 9:20: “Christ of God” or “Messiah of God.” This paper questions whether this is an overlooked example of Luke’s use of the filiation formula. How the filiation formula works grammatically in Greek is first explained. Then examples found in Greek inscriptions and literary texts are presented. Next, examples in the Septuagint are discussed. The paper then examines the use of the filiation formula in the New Testament, particularly in Luke’s genealogy in chapter 2. Bringing together these epigraphic and textual discussions related to the filiation formula, the paper then asks whether use of the formula has been overlooked in translations of Luke 9:20. Other possible uses of the filiation formula in Luke’s Gospel are also explored. By recognizing how the filiation formula is used in Greek texts, the paper can offer a fresh translation of Luke 9:20.