The verdict by Malaysia's highest court prevents Tuanku Ismail Petra Yahya Petra from regaining his throne of Kelantan state anytime soon.
Nine of Malaysia's 13 states are ruled by hereditary royal families.
Ismail's eldest son, Tengku Muhammad Faris Petra, took over the throne of the northern state in September while his father was bedridden with a reported stroke.
Ismail's lawyer, Rashid Zulkifli, said a three-judge panel in the Federal Court ruled Friday that the ex-sultan has no right to refer key legal questions about the extent of his son's powers while he was medically incapacitated.
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