  Exploiting the Kepler transit data, we uncover a dramatic distinction in the
prevalence of sub-Jovian companions, between systems that contain hot Jupiters
(periods inward of 10 days) and those that host warm Jupiters (periods between
10 and 200 days). Hot Jupiters, with the singular exception of WASP-47b, do not
have any detectable inner or outer planetary companions (with periods inward of
50 days and sizes down to $2 R_{\rm Earth}$). Restricting ourselves to inner
companions, our limits reach down to $1 R_{\rm Earth}$. In stark contrast, half
of the warm Jupiters are closely flanked by small companions. Statistically,
the companion fractions for hot and warm Jupiters are mutually exclusive,
particularly in regard to inner companions.
  The high companion fraction of warm Jupiters also yields clues to their
formation. The warm Jupiters that have close-by siblings should have low
orbital eccentricities and low mutual inclinations. The orbital configurations
of these systems are reminiscent of those of the low-mass, close-in planetary
systems abundantly discovered by the Kepler mission. This, and other arguments,
lead us to propose that these warm Jupiters are formed in-situ. There are
indications that there may be a second population of warm Jupiters with
different characteristics. In this picture, WASP-47b could be regarded as the
extending tail of the in-situ warm Jupiters into the hot Jupiter region, and
does not represent the generic formation route for hot Jupiters.
