  The Standard Model is a successful theory but lack of a mechanism for
neutrino mass generation as well as a solution to the naturalness problem. In
the models that are proposed to simultaneously solve the two problems, heavy
Majorana neutrinos and top partners are usually predicted that can lead to a
new decay mode of the top partner mediated by the heavy Majorana neutrinos:
$T\to b\,W^{+}\to b\,\ell^{+}\ell^{+}q\bar{q'}$. In this paper, we will study
the observability of such a new signature via the pair production process of
top partner $pp \to T\bar{T} \to 2b+ \ell^\pm \ell^\pm+4j$ in a model
independent way. By performing Monte-Carlo simulation, we present the $2\sigma$
exclusion limits of the top partner mass and mixing parameters at the HL-LHC.
