The political earthquake in Egypt has sent shockwaves through Israel, shredding decades-old security assumptions and leaving the Jewish state to face more turbulent, demanding relations with its powerful neighbour.
The toppling of President Hosni Mubarak following a popular uprising was greeted by scenes of jubilation in Cairo and wild celebrations on the streets of Gaza, but in Israel, yesterday's dramatic events were met with silent anxiety.
It is hard to overstate the importance to Israel of its 1979 peace accord with Egypt, which has given it stability on its southern flanks and has helped successive Israeli leaders maintain the status quo in the unresolved Palestinian conflict.
A future Egyptian government is unlikely to tear up the historic Camp David peace treaty, because such a move could deprive it of crucial USaid. However, most analysts foresee a more testy and uncomfortable ties in the years ahead.
"This has left us dangerously isolated. Egypt was our only strategic partner in the region," said Alon Liel, a former director-general of Israeli Foreign Ministry.
"In the future, Egypt will have different relations with Israel. More hostile and more unpredictable," he added.
Mubarak ruled Egypt for three decades, dealing with eight different Israeli prime ministers during that period and providing them a vital anchor of certainty as they continued to strike out against numerous enemies across the Arab world.
Egypt is the only Arab state to still have an ambassador in Israel and has played an important role in helping contain the Islamist group Hamas, which governs Gaza and has close links to the Muslim Brotherhood - a potential winner in Egypt's turmoil.
Hamas has already urged Cairo to relax its strict border controls with Gaza that Israel says are vital to prevent the flow of arms into the coastal enclave.
A new leadership in Cairo is bound to take time to settle in and it is impossible to predict at this stage who will hold the real power, but it seems very unlikely that whoever takes charge will continue with Mubarak's benign policy towards Israel.
Many Jewish leaders fear that Egypt will follow the path of Iran, which created an Islamic republic after the overthrow of the Shah and has threatened to wipe Israel off the map.
"Egypt is not a similar earthquake to Tunisia, but rather what happened in Iran," said Major General Aharon Ze'evi Farkash, a former director of military intelligence. "However, I think it will all take time, and we will be able to prepare."
If such a scenario plays out, it would jeopardise Israel's remarkable, recent economic expansion, which has given it per capita GDP of some $30,000 a year against just $6,200 in Egypt.
Agencies