Field Marshal Roberts hoisted the Union Jack over Bloemfontein on May 28 1900, and annexation became official on October 6. Sir Alfred Milner was appointed governor on January 4, 1901, with Hamilton Goold-Adams as lieutenant-governor.
By 1904 sentiment was growing for some form of self-government, and the Oranje Unie party was formed to promote the idea. In the following year Lord Milner retired and Lord Selborne became the new governor. The colony achieved self-government in 1907, and on November 27 Abraham Fischer of the Oranje Unie became its first Prime Minister. In 1910 it joined the Union of South Africa as the "Orange Free State Province".
Immediately upon annexation, the British overprinted the republic's stamps with "V.R.I." (Victoria Regina Imperatrix). There were many minor variations, some rare and prized today. Stamps of the Cape Colony were also overprinted, with "ORANGE RIVER COLONY" (August 10, before the colony officially existed), and only in 1903 did the Orange River Colony get its own stamps. These stamps featured a portrait of King Edward VII, along with small pictures of a springbok and a gnu. They were used until the union in 1910, and are generally readily available and inexpensive today.Postage stamps