  We present recent contemporaneous X-ray and optical observations of the
Be/X-ray binary system A\,0535+26 with the \textit{Fermi}/Gamma-ray Burst
Monitor (GBM) and several ground-based observatories. These new observations
are put into the context of the rich historical data (since $\sim$1978) and
discussed in terms of the neutron star Be-disk interaction. The Be
circumstellar disk was exceptionally large just before the 2009 December giant
outburst, which may explain the origin of the unusual recent X-ray activity of
this source. We found a peculiar evolution of the pulse profile during this
giant outburst, with the two main components evolving in opposite ways with
energy. A hard 30-70 mHz X-ray QPO was detected with GBM during this 2009
December giant outburst. It becomes stronger with increasing energy and
disappears at energies below 25\,keV. In the long-term a strong optical/X-ray
correlation was found for this system, however in the medium-term the
H$_\alpha$ EW and the V-band brightness showed an anti-correlation after
$\sim$2002 Agust. Each giant X-ray outburst occurred during a decline phase of
the optical brightness, while the H$_\alpha$ showed a strong emission. In late
2010 and before the 2011 February outburst, rapid V/R variations are observed
in the strength of the two peaks of the H$_\alpha$ line. These had a period of
$\sim$\,25 days and we suggest the presence of a global one-armed oscillation
to explain this scenario. A general pattern might be inferred, where the disk
becomes weaker and shows V/R variability beginning $\sim$\,6 months following a
giant outburst.
