A freely moving diamond trapped inside another diamond was discovered in Siberia by Alrosa in 2019. The unusual diamond, nicknamed the “Matryoshka” after the traditional Russian nesting dolls, attracted widespread interest in how this feature formed The 0.62 ct flat octahedral diamond, a twinned macle, was recently examined by the New York laboratory. Flat-bottom trigon etch pits were well developed on the face {111} (figure 1). The crystal showed a clear green bodycolor, with small dark green radiation stains in shallow fractures along the edges when viewed from the top of the crystal. Two etch channels on opposite sides of the edges had rectangular openings about 0.2 mm in width. The channels extended into the internal enclosed cavity. These features made this diamond unique. Trapped in the cavity was a small, flat diamond crystal with a hexagonal outline. The small diamond, covered with some green radiation stains on the surface, is entirely detached from its host crystal and can move freely inside. The surface of the small diamond was covered with groups of straight parallel striations following the diamond crystal symmetry. No etched trigons were observed on the surfaces of the small diamond (figure 2). Except for tiny foreign-material contaminations at the two entrances of the open channels, no other inclusions were observed in this crystal (figure 3).