Using data corresponding to an integrated luminosity of $1.3\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, we observe a narrow mass state decaying into $\ensuremath{\Upsilon}(1S)+\ensuremath{\gamma}$, where the $\ensuremath{\Upsilon}(1S)$ meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at $10.551\ifmmode\pm\else\textpm\fi{}0.014(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.017(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, which is consistent with that of the state recently observed by the ATLAS Collaboration.