More details in our publication: Gvaramadze, Maryeva, et al., MNRAS, 2019 I am grateful to grant support from Czech Science Foundation GA18-05665S and RFBR grant 19-02-00779. During our search for massive stars on late evolutionary stages in WISE archive we discovered a high-velocity runaway star CPD-64º 2731, associated with a horseshoe-shaped nebula. Its spectral type is O5.5Vn((f)) and projected rotational velocity is ≈300 km/s, which is extremely high for this spectral type. The kinematic age of ≈ 6 Myr, assuming it was born near the Galactic plane, exceeds its age derived from single star models by a factor of two. These properties suggest that CPD-64º 2731 is a rejuvenated and spun-up binary product. The geometry of the nebula and the almost central location of the star within it argue against a pure bow shock interpretation for it. Instead, we suggest that the binary interaction happened recently, thereby creating the nebula, with a cavity blown by the current fast stellar wind. This conclusion is supported by our results of 2D numerical hydrodynamic modeling. The main goal of our project is the search for evolved massive stars through the detection of their mid-IR circumstellar nebulae in Spitzer and WISE archives. The search has led to the discovery of many dozens of previously unknown nebulae. Some of them were found around newly identified massive stars, such as luminous blue variables and blue supergiants (e.g. Gvaramadze et al. 2010). Some others were interpreted as bow shocks produced by known or newly identified OB stars. During the search we discovered a horseshoe-shaped shell of angular radius of ≈30 arcsec in the Circinus constellation. We identified the nebula with the IRAS source 14032−6515, and found within it a massive star, known as CPD−64º 2731. The nebula has attracted out attention because it is associated with a high-velocity runaway main sequence O star, but does not look like a genuine bow shock. Using proper motion measurements for the star from Gaia DR2 we found that CPD−64º 2731 is a high-velocity (≈160 km/s ) runaway star with the vector of its space velocity inclined to our line of sight by ≈33º. The runaway status of CPD−64º 2731 is also supported by the large separation of this star from the Galactic plane of z≈0.5 kpc. CPD−64º 2731 moves almost perpendicular to the Galactic plane and its past trajectory intersects the Galactic plane at l ≈311.5º. In this direction our line of sight first crosses the Carina-Sagittarius arm at ≈1.5 kpc and then tangentially enters into the Crux-Scutum spiral arm at ≈5 kpc. All distance estimates for CPD−64º 2731 imply that this star was formed in the Crux-Scutum arm. The kinematic age of CPD−64º 2731 of ≈6 Myr, assuming that this star was born near the Galactic plane, exceeds its age derived from single star models by a factor of two. We therefore suggest that CPD−64º 2731 is a rejuvenated and spun- up product of binary interaction (a massive blue straggler). We have modeled the interaction between the stellar wind of CPD−64º 2731 and the ISM. To verify our hypothesis that CPD−64º 2731 is the binary interaction product we performed two types of simulation: - bow shock produced by a runaway star whose wind parameters and space velocity were set to be identical to those of CPD−64º 2731 - runaway star was assumed to be initially composed of two ≈20 M ⊙components with identical mass loss rate and wind velocity. After several thousand years, the wind parameters of the binary product were set to be equal to those of CPD−64º 2731, and the new, much faster, wind started to blow a bubble in the preceding slow wind material bounded in the upstream direction by the bow shock. The second scenario reproduces reasonably well the horseshoe shape of the nebula around CPD−64º 2731 and confirms our hypothesis Spectra were obtained with the SALT High Resolution Spectrograph. For modeling we used the stellar atmosphere code CMFGEN (Hillier & Miller 1998). Spectral analysis of da