Many large black triangle UFO’s have been seen all over the world. From the famous Phoenix Lights incident and the wave of sighting over Belgium, Austria.
There are those who claim the triangle ufo’s are built and operated by top-secret military defense contractors operating under highly classified black budget projects.
There’s a lot of leaked information and videos which many claim is the TR3-B Aurora or Mantis.
I believe some are top-secret military crafts and others are anti-gravity crafts operated by the advanced breakaway civilizations that share the planet with us.