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Binary millisecond pulsar systems are superb probes of stellar, binary evolution and the physics of extreme environments. The location of millisecond pulsars relative to the `spin-up line' in the spin period and spin-down rate (P-Ṗ) diagram plays a critical role in understanding population studies of radio millisecond pulsars and accreting neutron stars in X-ray binaries. Here we report the discovery of the pulsar PSR J0435+3233, which exhibits an exceptionally high spin-down rate of 4.8775101(2) × 10<SUP>-17 </SUP>s s<SUP>-1</SUP>—two orders of magnitude higher than that of other known millisecond pulsars, thus occupying a distinctive position in the P-Ṗ diagram. This discovery implies a formation channel that differs from the classical evolutionary path, challenging the theoretical models of the recycling process and placing stringent constraints on spin-up theories. One plausible scenario is that its progenitor was a neutron star undergoing super-Eddington accretion, with the currently observed pulsar being a remnant of such a system. Another possible mechanism is its formation through the accretion-induced collapse of a magnetized ONeMg white dwarf, although this scenario requires specific theoretical assumptions. Hence, PSR J0435+3233 has an important impact on binary evolution theory.