Dear colleagues, I have just completed the analysis of my unfiltered CCD observations of TCP J21382907+4146190 (aka AT 2025sss), obtained on 2025 Aug 12/13 at CBA Extremadura Observatory. The data were collected under clear skies using a 0.40-m f/5.1 telescope and a Moravian G2-4000 CCD. I have been observing this object nightly since Aug 02nd with only one night missed. TCP J21382907+4146190 was discovered by Yuji Nakamura (Japan) on Aug 01.55 UT. It has a g=22.6 mag counterpart, implying an outburst amplitude of ~8.5 mag. Until last night, no clear modulations were visible in the light curves. The Aug 12/13 light curve now shows clear ordinary superhumps with an amplitude of 0.16 mag. Given their late onset (11 days after detection) and the large outburst amplitude, we conclude that TCP J21382907+4146190 is a new WZ Sge-type dwarf nova. A period analysis, using ANOVA, Lomb-Scargle, Generalized-Lomb-Scargle and PDM methods (Peranso 3.1) yields a combined superhump period of 0.0640 +/- 0.0012d. The object was measured at mag CV = 14.9 on Aug 12th. Image calibration and photometry were performed with the latest release of Phoranso. Further observations are strongly encouraged to refine the superhump period. I will submit my observations to AAVSO, CBA and VSNET for further analysis. With kind regards, Tonny --- Tonny Vanmunster CBA Belgium Observatory CBA Extremadura Observatory http://www.cbabelgium.co <http://www.cbabelgium.com/> m PERANSO : The Light Curve and Period Analysis Software http://www.peranso.co <http://www.peranso.com/> m PHORANSO: Photometric Reduction and Analysis Software http://www.phoranso.com <http://www.phoranso.com/>