Readers might - might - be forgiven for thinking that Antipopes are a feature of Papal history from the latter part of the first millennium, or from the clash of Papacy and Empire over the matter of Investiture, or from the Great Schism and the Conciliar era. The conventional historical case would point to ‘Felix V’ of the House of Savoy - elected by the Council of Basle - as the last Antipope, and that was in the mid-fifteenth century.
However this is not case. I recall a discussion in my early days in Oxford about the several claimants to the Papal throne we could then call to mind. A conversation yesterday led me to a Wikipedia article which catalogues the recent and current Antipopes - or if you are a follower of one or other of them, the true Pope - and here I was surprised to find just how many there are or have been in recent decades.
The plurality of ‘Peter II’ does not make for clarity, nor potentially perhaps for peace of mind, as Peter II is the name in the St Malachy prophetic tradition for the Pope of the End Times... Here too are Peter III, several Gregory XVIIs and Leo XIVs plus Alexander IX, Adrian VII, Clement XV, Linus II, Pius XIII, plus other names, some without precedent, in Papal history. All useful Catholic conversational trivia when passing the port...
The listings, divided between Concalvists and Mysticalists, can be seen at Conclavism