They're the political twins that have dominated Irish politics for a century - Fianna Fáil and Fine Gael, sworn enemies whose mutual loathing has driven every general election, whose combined share of the vote was so high that other parties got squeezed out.
And now everything has changed - because the division that began in Civil War in 1922 has now been buried, and the two bitter rivals are going to share power.
The original division was over the Treaty that ended the War of Independence - opponents said it was a betrayal of the Republic, supporters said it was a stepping stone towards complete freedom.
Now that issue was settled - by de Valera’s 1937 constitution which made Ireland a republic in all but name, and by the declaration of the Republic in 1948 by a Fine Gael-led government, when the country formally left the British Commonwealth.
But the rivalry remained. There’s not much fundamental difference on economic policy, though there are differences of perception - Fine Gael sees Fianna Fáil as slightly untrustworthy, Fianna Fáil sees Fine Gael as out of touch with ordinary people.
But now, for better or worse, they’re going to have to learn to get over those differences, and to work together.