Philip in A.A.R.M.
Philip Lipton is the son of Dwight K. Schrute and Angela Martin. He was born on February 2nd, 2012. Philip is named after one of Angela's favorite cats. Pam Halpert, whose second pregnancy overlapped with Angela's pregnancy with Philip, also named her son Philip as a tribute to her late grandfather.
Initially, Dwight believes that Philip is his own son, and in "Portrait Studio", he steals one of Philip's diapers and takes it for paternity testing; however, it is later stated in an interview that the test eventually proved that Philip is, in fact, not Dwight's son. In "A.A.R.M." Angela reveals to Dwight that Philip is indeed his son. It is currently unclear how Angela was able to make Dwight believe that he was not the father after paternity testing, but, considering the fact that Jim and Pam's son had been brought to the office, it is likely that he simply brought the wrong diaper for testing.