Thai officials often quietly remind journalists that Crown Prince Vajiralongkorn is the undisputed heir to the throne, citing the 1924 palace succession law and his investiture in 1972.
The harsh lese majeste law prevents any open discussion of the succession, but that has not stopped clandestine gossip in Thailand about "alternative scenarios", usually involving the crown prince's popular sister Princess Sirindhorn.
This rare appearance at such a high-profile, public event by the Crown Prince - heavily promoted by the military government - will send out a clear signal that he has the backing of the armed forces, and that he can be a "man of the people", like his father.
It also shows him as a loving and dutiful son. With King Bhumibol in increasingly frail health after 69 years on the throne, the military is pre-occupied with managing an orderly succession; indeed that may have been uppermost in the generals' minds when they launched last year's coup