The continent of Antipodia (OTL Australia / Oceania) stayed undiscovered for anyone but its aboriginal inhabitants for many centuries.
During the third voyage of Chinese Treasure Ships (1407-09, that's 3104, Yin Fire Pig / 3106, Yin Earth Ox) they went east, to Brunei, Majapahit, and even discovered the north coast of Australia (although they weren't interested in the latter).
In 1570, Nipponese ships trading with Java discovered the north coast too, but weren't interested in this land, like the Chinese and Javans who came before them. In the year of 1612, traders from the sultanate of Brunei discovered the continent again, weren't interested either.
1644, the first Europeans arrived when the Swedes discovered the west coast. Still, they weren't interested in that continent either.
In 1704, English ships went west from Cape Hoorn, (re-)discovered Australia and New Zealand, which were called Antipodia and New Albion respectively. England took claim of these lands, but for quite some while they stayed in the shadow of the English colonies in North and South Atlantis. Only after the latter were lost in the anti-British War, more settlers would arrive. While English settlers preferred New Albion (in fact, these islands were reserved for them), Irish went to Antipodia itself instead, choosing a life as shepherds. They soon had the clear population majority in Antipodia's thinly settled North, South and West, and a smaller majority (60%) in the South-East. When the Potato crisis happened in Ireland in 1849, so many of them emigrated to Antipodia that its population more than doubled in short time.
1850, after the British revolution, the Irish rebelled in Antipodia, kicked out the English, who only kept control of OTL Tasmania. The continent was renamed Tir Tairngire (non-Irish people preferred to speak of Tirland, however).