^^ In most of the King's obligations and ceremonies, Yes, He did and still does :
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In Thailand the Crown Prince and his consort (3rd wife) hold many royal engagements together. But somehow, They rarely appear together in the events outside Thailand.
The CP's 2nd wife is Sucharini Vivajrawongse, Currently lives in the US with her sons Chudhavajra, Vajaresra, Chakrivajra and Vajravira. Her last child with the CP is Princess Sirivannavari who ,only child and only daughter, still hold a royal title. In late 1990s, Sucharini and the 4 princes were mysteriously renounced their royal titles by the palace. They are forgotten by the Thai society nowadays.
Crown Prince Maha Vajiralongkorn, Mom (a Thai royal title) Sucharini Vivajrawongse and their children. Source
The CP is going the succeed the throne for sure because his older sister,
Princess Ubolratana Rajakanya, is forbidden to succeed the throne by
The 1924 Palace Law of Succession since she once married to a foreigner. (
Section 11 states: "Descendants of the royal family with any of the following characters shall be excluded from the line of succession: Married to a foreign consort;")