By Magdi Abdelhadi
BBC News Arab affairs analyst
Political assassinations are not new in Lebanon.
Gemayel's grandfather, also called Pierre, founded the Phalangists
The killing of Mr Gemayel is the latest in a series of attacks targeting anti-Syrian politicians in Lebanon over the past two years.
This has plunged the country in a deep political crisis from which it still cannot recover.
In fact, killing Mr Gemayel appears to have its roots in last year's assassination of the former Prime Minister, Rafik Hariri.
The Lebanese cabinet has been split over whether to endorse a United Nations plan to set up an international tribunal to try those suspected of the killing, which included senior Syrian and Lebanese officials.
Syria has denied any involvement. Mr Gemayel and his colleagues from the anti-Syrian block endorsed the plan, much to the anger of the pro-Syrian ministers on the cabinet, who resigned in protest.
Fear of reprisals
As a result, the pro-Syrian Hezbollah movement threatened to stage a series of protests with the aim of bringing the government down.
Anti-Syrian politicians warned that the issue may spark a new wave of assassinations against them.
It appears that their worst fears have now been borne out by the killing of Mr Gemayel.
The killing of ex-PM Rafik Hariri has led to instability in Lebanon
Being anti-Syrian, they have pointed the finger at Damascus, as they did after last year's assassination of Mr Hariri.
But Syria has condemned the killing as a foul crime.
The fear now is that the killing of Mr Gemayel could lead to retaliation from his supporters. He comes from a well-known Christian family and was named after his grandfather, who founded one of Lebanon's most powerful Christian political organisations: the Phalangist party.
His father, Amin, is a former president, and so was his uncle, Bashir, who was assassinated in 1982, apparently for co-operating closely with Israel during the civil war.
The Phalangists are staunchly pro-Western and remain opposed to the pan-Arab ideology of Syria and its allies inside Lebanon.