Abstract: In the presence of a gray market, brand owners face significant challenges, including sales diversion, brand image erosion, and decreased market trust. Optimizing selling strategies to enhance brand decisions and profits is crucial. This study examines a two-stage supply chain involving a brand that simultaneously sells two complementary products and a gray market speculator. A two-stage sequential game model, positioning the brand as the leader, is constructed. The analysis explores four selling strategies, focusing on the effects of product complementarity, market potential, and gray product discount coefficients on brand profits and optimal strategies. The findings indicate that when the potential scale disparity between the two complementary products in the high-priced market is significant, product complementarity is low, and the gray product discount coefficient is high, the brand should implement a pure bundling selling strategy in the low-priced market and a separate selling strategy in the high-priced market. Conversely, a separate selling strategy should be employed in the low-priced market and a pure bundling selling strategy in the high-priced market.