Hanjie Tan (Institute of Astronomy, National Central University), Mi Zhang, Guoyou Sun, Jingyuan Zhao (Xingming Observatory), Quanzhi Ye , Xing Gao (Xingming Observatory), report the outburst in a CV or SN candidate (15.83 r). The transient was discovered on several 120-s survey images (limiting mag about 18.0) taken by Xing Gao at Xingming Observatory #3 (N88) around Apr. 10.82413, 2021 UT using a unfiltered CCD (0.3-m f/3.6 reflector). Images can be found at: http://xjltp.china-vo.org/xm66ht.html
XM66HT C2021 04 10.82413 19 15 47.00 +41 31 00.3 15.83 r N88
