Owned by Sheikh Mohammed Obaid, King Bolete won his seasonal bow at Ascot last month and improved to win again off a 4lb higher mark.
Jockey Andrea Atzeni adopted front running tactics and King Bolete raced enthusiastically at the head of affairs.
Andrea judged the pace to perfection and quickened the tempo with half a mile to run.
The runner-up Tawdeea put up a sustained challenge but King Bolete was always holding that rival and went on to win by half a length.
Roger said: "He has done it nicely. He is an improving four-year-old who stays very well. He bounces off the fast ground and is progressive. We may look to come back for the Old Newton Cup."