\begin{document}$ B^{-}\to\pi^{+}\pi^{-}\ell^{-}\bar\nu_\ell $\end{document}, with \begin{document}$ \ell=e $\end{document} or μ. Using the newly available data across the full \begin{document}$ \pi\pi $\end{document} invariant-mass spectrum, we determine the non-resonant \begin{document}$ B\to\pi\pi $\end{document} transition form factors. We obtain a non-resonant branching fraction \begin{document}$ {\cal B}_N(B^{-}\to\pi^{+}\pi^{-}\ell^{-}\bar\nu_\ell)=(3.5\pm 1.4^{+4.3}_{-2.4})\times 10^{-5} $\end{document}. This result indicates that the non-resonant contribution can be comparable in magnitude to the resonant components and should not be treated as a negligible background in precision measurements. Our findings highlight the importance of dedicated experimental efforts at Belle II and LHCb to further probe the non-resonant contribution."> Semileptonic <inline-formula><tex-math id="M1">\begin{document}${B^{-}\to\pi^{+}\pi^{-}\ell^{-}\bar\nu_\ell}$\end{document}</tex-math></inline-formula> decay over the full <inline-formula><tex-math id="M2">\begin{document}${\pi\pi}$\end{document}</tex-math></inline-formula> invariant mass spectrum -
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