A recently rediscovered work of exceptional rarity, this portrait situates Bronzino at the precise threshold between apprenticeship and mastery, offering collectors a singular opportunity to acquire one of the earliest known examples of his portraiture. Painted during the period of his closest association with Jacopo Pontormo, the composition carries the muted tonal elegance and psychological self-containment characteristic of that intimate working relationship, while already demonstrating the technical command and cool precision that would define Bronzino's mature manner. The sitter regards the viewer with an expression of studied detachment, his hand resting on a book in a gesture that signals intellectual identity, a device Bronzino would refine across the decades to come. Executed in oil on panel at 94 by 78 centimetres, the work possesses the surface finish and formal authority that Giorgio Vasari, Bronzino's first biographer, described in 1568 as executed with incredible diligence, finished so well that nothing more could be desired. The portrait's early provenance places it within the Corsini Gallery in Florence, where nineteenth-century guidebooks recorded it beginning with Federigo Fantozzi's 1842 listing, initially under an attribution to Andrea del Sarto. A subsequent reattribution to Pontormo followed in Ulderico Medici's 1886 catalogue of the collection, and the work has since been firmly associated with Bronzino through scholarly investigation, including a dedicated essay by Dr. Carlo Falciani. This arc of attribution, moving from del Sarto through Pontormo and arriving at Bronzino, reflects how thoroughly the young painter absorbed the visual language of his milieu before transcending it. By the early 1540s, Bronzino would be appointed official court painter to Cosimo de' Medici, producing works of European-wide influence, but this panel preserves something rarer, the moment just before that ascent crystallised. For collectors of Old Master paintings, the work carries the additional weight of historical scarcity. Renaissance portraits of this quality and documented lineage remaining in private hands represent a diminishing category, and portraits attributable to Bronzino's earliest phase are rarer still. The influence of his mature portraiture extended across more than a century of European court painting and continued to captivate artists as varied as Ingres, David, Frida Kahlo, and Picasso, testament to the enduring authority of his formal solutions. This panel, now offered at Christie's Old Masters, stands as an eloquent prologue to that entire tradition, a work in which the foundations of one of the Renaissance's most celebrated portrait careers are visibly, compellingly being laid.