  We report the discovery of a new Wolf-Rayet star in Aquila via detection of
its circumstellar nebula (reminiscent of ring nebulae associated with late WN
stars) using the Spitzer Space Telescope archival data. Our spectroscopic
follow-up of the central point source associated with the nebula showed that it
is a WN7h star (we named it WR121b). We analyzed the spectrum of WR121b by
using the Potsdam Wolf-Rayet (PoWR) model atmospheres, obtaining a stellar
temperature of ~ 50 kK. The stellar wind composition is dominated by helium
with ~ 20 per cent of hydrogen. The stellar spectrum is highly reddened
(E_{B-V} = 2.85 mag). Adopting an absolute magnitude of M_v = -5.7, the star
has a luminosity of log L/Lsun = 5.75 and a mass-loss rate of 10^{-4.7}
Msun/yr, and resides in a distance of 6.3 kpc. We searched for a possible
parent cluster of WR121b and found that this star is located at ~ 1 degree from
the young star cluster embedded in the giant HII region W43 (containing a
WN7+a/OB? star -- WR121a). We also discovered a bow shock around the O9.5III
star ALS9956, located at ~ 0.5 degree from the cluster. We discuss the
possibility that WR121b and ALS9956 are runaway stars ejected from the cluster
in W43.
