BEIRUT — Lebanese Christian politician Samir Geagea backed his rival Michel Aoun for the presidency on Monday, in an apparent break with his Saudi-backed allies that aligns him with a civil war era enemy supported by Hezbollah.

The announcement edges 80-year-old Aoun closer to the presidency vacant for 20 months and marks a rare show of unity in a Christian community riven by divisions for years. The presidency is reserved for a Maronite Christian.

Geagea made the announcement in a televised news conference sitting alongside Aoun. He also called on his allies in the March 14 alliance, led by the Saudi-backed politician Saad al-Hariri, to support Aoun’s candidacy.