  The discovery of Weyl semimetals (WSMs) has fueled tremendous interest in
condensed matter physics. WSMs require breaking of either inversion symmetry
(IS) or time-reversal symmetry (TRS); they can be categorized into type-I and
type-II WSMs, characterized by un-tilted and strongly tilted Weyl cones
respectively. Type-I WSMs with breaking of IS or TRS and type-II WSMs with IS
breaking have been realized experimentally, but TRS-breaking type-II WSM still
remains elusive. In this article, we report an ideal TRS-breaking type-II WSM
with only one pair of Weyl nodes observed in the antiferromagnetic topological
insulator Mn(Bi1-xSbx)2Te4 under magnetic fields. This state is manifested by a
large intrinsic anomalous Hall effect, a non-trivial $\mathrm{{\pi}}$ Berry
phase of the cyclotron orbit and a large positive magnetoresistance in the
ferromagnetic phase at an optimal sample composition. Our results establish a
promising platform for exploring the physics underlying the long-sought, ideal
TRS breaking type-II WSM.
