apocryphal - (of a story or statement) of doubtful authenticity, although widely circulated as being true.

apocryphal - 

əˈpɒkrɪf(ə)l/

adjective

1. (of a story or statement) of doubtful authenticity, although widely circulated as being true.

   "an apocryphal story about a former president"

   synonyms:

   fictitious, made-up, untrue, fabricated, false, spurious; More

   • of or belonging to the Apocrypha.

     "the apocryphal Gospel of Thomas"