Two thousand million or so years ago...
two galaxies were colliding; or, rather, were passing through each other. A couple of hundreds of millions of years either way do not matter, since at least that much time was required for the inter-passage. At about that same time - within the same plus-or-minus ten percent margin of error, it is believed - practically all of the suns of both those galaxies became possessed of planets.
Doc Smith, Triplanetary
Be afraid. Be very afraid...