unauthentic

/ˌʌnəˈθɛntɪk/
adjective
  1. Not genuine, real, or true; fake.
    • The museum discovered that the painting was unauthentic and returned it to the seller.
    • The signature on the document was ruled unauthentic by the handwriting expert.
    • She felt the smile on his face was unauthentic, hiding his true feelings.