Thailand Rajaguru (one with Red shawl in 1st pic) along with some Brahmins of thailand meets Jagadguru Shankaracharya of Kanchi Mutt. Photos belong to year 2015.
Even today, the coronation of Thai Buddhist king is conducted by the Brahmin Rajaguru.
@HinduTrad

Here in this pic, the Rajguru is seen reading some sort of document (i think its the kings duties and vows like a शपथ-पत्र) in front of the newly coronated king. This happened in 2019.

The Maharajguru of Thailand, Phra Guru Bidhi Sri Visudhigun, belongs to the Vasishtha Gotra and conducts various rituals including the Triyampawai Ceremony in the Thailand Royal Court. His ancestors belonged to South India and have deep connections with Kanchipuram.

Triyamppawai ceremony is identified with Tiruvempavai (திருவெம்பாவை), which is a 9th century Tamil Saivite Hyms composed by Tamil saivite brahmin saint Manickavasagar. It forms a part of the Tamil Saivite Bhakti literature called பன்னிரு திருமுறை (12 Tirumurais)

Tiruvempaavai is the early morning wake up Suprabatha hym sung for Lord Shiva on Tamil month Margazhi (Margashirisha). Tiruvempavai hyms were composed in Annamalaiyar Shiva Temple in Tiruvannamalai.

It is believed that Thiruvempavai was introduced to Thailand by Tamil brahmins who immigrated to then Siam in 14th century CE. Available historical evidences confirm that Thiruvempavai has been observed at Ayutthaya, Sukhothai and Sawankhalok, the ancient Thai capital cities.

Initially it was observed as a penance and fasting at Sawankhalok and Phitsanulok and later it got royal patronage and became one of the 12 royal ceremonies combined with the swing ceremony.

The annual Giant swing ceremony was held in major cities until 1935, when it was abolished for safety reasons. However the Tiruvempavai hyms continue to be recited even today by the priests in Thailand.

Along with Tiruvempavai, Tiruppavai, a Vaishnavite hym compsed by Vaishnava azhwar saint Andal in 8th century is also recited.
Tiruppavai comes under the 4000 Divya Prabandham canon, which is revered by Shri Vaishnavas of south india as Dravida Veda.

Image of the Giant swing Sao Ching Cha in Bangkok associated with the royal ceremony of Triyamphway.

Image of the Thewasathan Bot Phram (Devasthan) or the Royal Brahmin Office of Thai Royal Court near Wat Suthat in the Phra Nakhon District, Bangkok, Thailand. The Giant Swing mentioned in previous tweet, is located outside in front of this temple.

The temple is the official centre of Hinduism in Thailand. The temple is the home of the Court Brahmins, who are descended from an ancient lineage of priests from Rameswaram, Tamil Nadu. The temple was founded in 1784 by King Rama I, the founder of the Chakri dynasty.

The temple is dominated by three large rectangular buildings, on an East to West axis. Each of the three white structures is a shrine dedicated to a particular Hindu deity. More on the temple deities in following tweets.

The Ho Phra Isuan dedicated to Shiva is located to the south. On the altar in the shrine is a large Lingam shrouded in flowers. The Lingam is thought to date back to the sixth century. Next to the Lingam on the altar is a statue of Shiva dancing in a ring of fire (Nataraja).

The Ho Phra Phikkhanesuan Shrine dedicated to Ganesha is located in the middle. The shrine contains five statues of sitting Ganesha, made of granite, sandstone, bronze and two of green stone.

The Ho Phra Narai Shrine dedicated to Vishnu is located in the north. The shrine contains a large statue of Vishnu and a smaller statue of Lakshmi and Bhūmi (Vishnu's wife).

A small outdoor shrine to Phra Phrom Shrine is dedicated to Brahma.