  The very recently observed $D^{\ast}_{sJ}(2463)$ meson is described as a
$J^{P}=1^{+}$ $c\bar{s}$ bound state in a unitarised meson model, owing its
existence to the strong OZI-allowed $^{3}P_{0}$ coupling to the nearby $S$-wave
$D^{\ast}K$ threshold. By the same non-perturbative mechanism, the narrow
axial-vector $D_{s1}(2536)$ resonance shows up as a quasi-bound-state partner
embedded in the $D^{\ast}K$ continuum. With the same model and parameters, it
is also shown that the preliminary broad $1^{+}$ $D_{1}(2400)$ resonance and
the established narrow $1^{+}$ $D_{1}(2420)$ may be similar $c\bar{n}$
partners, as a result of the strong OZI-allowed $^{3}P_{0}$ coupling to the
nearby $S$-wave $D^{\ast}\pi$ threshold. The continuum bound states
$D_{1}$(2420) and $D_{s1}(2536)$ are found to be mixtures of 33% $^{3}P_{1}$
and 67% $^{1}P_{1}$, whereas their partners $D_{1}(2400)$ and
$D^{\ast}_{sJ}(2463)$ have more or less the opposite $^{2S+1}P_1$-state
content, but additionally with some $D^{\ast}\pi$ or $D^{\ast}K$ admixture,
respectively.
  The employed mechanism also reproduces the ratio of the $K_{L}$-$K_{S}$ mass
difference and the $K_{S}$ width, by describing $K_{L}$ as a bound state
embedded in the $\pi\pi$ continuum. The model's results for $J^{P}=1^{+}$
states containing one $b$ quark are also discussed.
