In this April 26, 2012 file photo shows Christian Lebanese Forces party leader Samir Geagea during an interview with AFP at his house in Maarab, northeast of Beirut.

Lebanese Christian politician Samir Geagea will back his rival Michel Aoun for the presidency on Monday, local media reported, an apparent break with his allies that aligns him with a civil war era enemy supported by Hezbollah.

Media cited Melhem Riachy, a media official in Geagea’s Lebanese Forces Party, as saying Geagea would state his support for Aoun’s candidacy at a news conference later on Monday.

The move boosts Aoun’s chances of filling the presidency that has been vacant for 20 months, but does not guarantee him the post. Beyond his existing allies, among them the Iran-backed Hezbollah, Aoun needs the backing of other groups to secure the necessary parliamentary backing.

The Lebanese president, who must be a Maronite Christian, is elected by Parliament. Geagea’s move was a rare show of unity in a Christian community riven by political divisions for years. Geagea and Aoun took up arms against each other in the 1975-90 civil war in the so-called “war of elimination.”

Geagea’s move may also kill off an initiative tabled by his ally Saad Al-Hariri that would have resulted in another Maronite politician, Suleiman Franjieh, becoming head of state in a power-sharing agreement.

Aoun and Geagea, head of the two largest Christian parties in Lebanon, both opposed the Hariri initiative.

The Hariri initiative is widely thought to have angered Geagea, who had until that moment been the stated presidential candidate of Hariri’s March 14 alliance forged in 2005 from groups opposed to Syrian influence over Lebanon.

Aoun is part of the rival March 8 alliance that includes Hezbollah and the influential Amal Movement led by Parliament Speaker Nabih Berri.

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