Among the distinguishing characteristics of the remarkable hot R Coronae Borealis star DY Centauri, which was recently found to be a spectroscopic binary, is the presence of nebular forbidden lines in its optical spectrum. A compilation of photometry from 1970 to the present suggests that the star has evolved to higher effective temperatures. A comparison of spectra from 2010 with earlier spectra has shown that between 2003 and 2010, the 6717 and 6730 Å emission lines of [S II] underwent a dramatic change in their fluxes. This suggests that there was an increase in the nebula's electron density from 290 to 3140 cm-3 between 1989 and 2010, while the stellar temperature increased from 19 500 to 25 000 K. The nebular radius is about 0.02 pc, which is 60 000 times larger than the semimajor axis of the DY Cen binary system. The rapid changes of stellar temperature and the nebula's response to these changes demonstrate stellar evolution in action.