Ireland was already Christian, though, whereas Prussia and Lithuania were still pagan at this date.
But iirc the Vatican still regarded the Irish Church as heterodox in various ways, hence the Papal Bull granted to Henry II.
Ireland was already Christian, though, whereas Prussia and Lithuania were still pagan at this date.
Spain becomes a slightly stronger country by the mid-1500s. One way to go about this is earlier union of the Iberian crowns.
In the Anglo-Spanish war of the late 1500s, Spain's navy is stronger than in OTL. Spain is the clear victor in the war, and the peace treaty gives all of Ireland excluding The Pale to Spain. No other changes are different to OTL.
Spain consolidates its rule over Ireland, using it as a useful source of food, and forces heavy Hispanicization of the Irish, much as England did IOTL.
By the present day, Ireland is divided into The Pale, a British province on the central east coast, and Irlanda, an autonomous region of Spain, covering the rest of Ireland. The culture retains some Irish traits and it is populated by Irish people, some of whom desire independence, but in general it is a Spanish-speaking Catholic country similar to the rest of Spain.
An Ireland without English colonialism easily fulfills the requirements of the OP. England being weaker is probably the easiest way to achieve this. A failed Harrying of the North could lead to a Danish-aligned Anglo-Saxon North England, a Norman South England whose interests are mostly in France, and Welsh petty kingdoms in Wales. If this situation persists long enough, it could give some enterprising Irish warlord enough time to unite and centralize the island.
I'm not sure that's even necessary. Even IOTL English kings were generally too preoccupied elsewhere to expend much effort in Ireland, and English rule was limited to a small area around Dublin for most of the pre-Tudor period. Absent the need to defend the Pale, I doubt that many if any English monarchs would give much thought to the poor, boggy, out-of-the-way island to their west.