Which country's old royal capital was Luang Prabang?

Laos, officially the Lao People's Democratic Republic (LPDR), is a country in Mainland Southeast Asia, and the only landlocked country in Southeast Asia. It is bordered by Myanmar and China to the northwest, Vietnam to the east, Cambodia to the southeast, and Thailand to the west and southwest. Laos has a population of more than 7.5 million, and its capital and most populous city is Vientiane. It has three UNESCO World Heritage Sites: the town of Luang Prabang, the temple complex of Vat Phou, and the Plain of Jars. The 2021 completion of the Boten–Vientiane railway, Laotian section of the Laos–China Railway, connects Vientiane to Kunming. Laos participates in the Greater Mekong Subregion economic cooperation programme and is a member of ASEAN, the Asia-Pacific Trade Agreement, East Asia Summit, La Francophonie, and the World Trade Organization.