Thousands of Thai cyclists have joined Crown Prince Maha Vajiralongkorn in a ride through Bangkok in honour of his mother, Queen Sirikit.
Wearing shirts in the queen's colour - sky-blue - and emblazoned with "Bike for Mom", the cyclists paraded through streets closed to traffic.
Many Thais outside the capital were expected to do the same.
The queen - who turned 83 four days ago - is in very frail health, like the king, and will not be seen.
Commentators say the 43km (27-mile) cycle is the first event to be publicly led by the prince, who is 63.
About 300,000 people registered to join the ride.
The crown prince was followed by other well-known figures including Prime Minister Prayuth Chan-ocha and his cabinet.