Thousands of pro-democracy protesters in Thailand clashed with the motorcade carrying King Maha Vajiralongkorn as it passed through capital Bangkok.
Protesters were pushed back by ranks of police, raised the three-finger salute that has become a symbol of the protest movement.
They have called for curbs on the king’s powers and for the resignation of Prime Minister Prayuth Chan-ocha.
The protests on Wednesday follow months of escalating tension in the country.
The king, who spends most of his time abroad but has returned from Germany after several weeks, travelled in a car alongside Queen Suthida through a crowd of peaceful protesters, who chanted and raised their hands in the three-finger salute. The gesture is thought to have been inspired by the Hunger Games films in which it is used as a symbol of unity and defiance.
The royal couple were on their way to a Buddhist ceremony on Ratchadamnoen Avenue, where demonstrations had took place earlier in the day, before the protesters moved on towards Government House.
Supporters of the monarchy, dressed in t-shirts in royal yellow colour, staged rival protests in the capital, with some filmed violently attacking the pro-democracy protesters.
The growing student-led protest movement, which began in July, has become the greatest challenge in years to Thailand’s ruling establishment. Protests over the weekend in the capital were some of the largest in years, with thousands defying authorities to gather and demand change.
Authorities say 18,000 people joined Saturday’s demonstration, although others gave higher figures. Many stayed to continue the protest into Sunday before dispersing.
Demonstrators have demanded that the government headed by Prime Minister Prayuth, a former army chief who seized power in the coup, be dissolved; that the constitution be rewritten; that the authorities stop harassing critics and royal reform are particularly sensitive in Thailand, where criticism of the monarchy is punishable by long prison sentences.