  Mixed-morphology supernova remnants (MMSNRs) are characterized by a
shell-like morphology in the radio and centrally-peaked thermal emission in the
X-ray band. The nature of this peculiar class of supernova remnants (SNRs)
remains a controversial issue. In this work, by pairing the predictions of
stellar evolution theory with two-dimensional hydrodynamic simulations we show
that the mixed morphology properties of a SNR can arise by the interaction of
the SNR with the circumstellar medium shaped by a red supergiant progenitor
star, embedded in a dense environment. As a study case, we model the
circumstellar medium formation and the subsequent interaction of the SNR with
it of a $15~\rm M_{\odot}$ progenitor star. The reflected shock, formed by the
collision of the SNR with the density walls of the surrounding circumstellar
cavity, accumulates and re-shocks the supernova ejecta at the center of the
remnant, increasing its temperature so that the gas becomes X-ray bright. Such
a formation mechanism may naturally explain the nature of MMSNRs resulted from
Type II supernovae without the demand of additional physical mechanisms and/or
ambient medium inhomogeneities. We discuss alternative evolutionary paths that
potentially could be ascribed for the MMSNR formation within the framework of
the reflected shock model.
