Proper noun
The Lord High Commissioner to the General Assembly of the Church of Scotland, the representative of the Scottish (later British) monarch to the established church of Scotland appointed annually since 1690.
(historical) The Lord High Commissioner to the Parliament of Scotland, the representative of the Scottish (later British) monarch to the separate government of Scotland appointed intermittently between 1603 and 1707.
(historical) The Lord High Commissioner of the Ionian Islands, the representative of the British monarch appointed intermittently between 1815 and 1864.
Source: en.wiktionary.orgAn official statement released by explains that the Lord High Commissioner represents the sovereign at the Assembly after being appointed by the monarch “on the advice of the Prime Minister”. Source: Internet
Thus, on 21 May, by proclamation of the Lord High Commissioner, the Ionian Islands were united with Greece. Source: Internet