Butyriboletus regius (formerly Boletus regius), commonly known as the royal bolete or red-capped butter bolete, is a basidiomycete fungus of the genus Boletus found in China, Europe, and North America. B. regius has a pink cap, yellow flesh, and a reticulate pattern on the stem. Harry D. Thiers described a similar mushroom from California as B. regius, although it has yet to be shown to be the same species. B. regius in Europe does not stain when exposed to air, or stains weakly, but the California species stains blue. Both European and California specimens are considered choice edibles.