First (210) and second (240) feedstocks are hydrotreated in an integrated hydrogenation plant (200) using a hot separator (230) that provides a vapor stream containing at least some of the hydrotreated first feedstock (210), wherein the second feedstock (240) is mixed with the vapor stream at a position downstream of the separator (240) and upstream of the a second hydrotreating (250) reactor to form a mixed second feedstock that is fed into the second hydrotreating reactor (250) to produce a ultra-low sulfur product.