It appears that Silvio Berlusconi's long stretch of good luck has finally run out: Late Thursday, the three-time Italian prime minister and dominant force in Italian politics was handed a final conviction in a tax-fraud case. The Court of Cassation, Italy's top criminal court, upheld Berlusconi's conviction and four-year prison sentence, declaring both rulings "irrevocable."

Appearances might be deceiving, though. Berlusconi's four-year prison sentence has already been reduced to one under an amnesty law aimed at reducing Italy's prison overcrowding. And because he's 76 and this is the first conviction that has stuck, there's a good chance that the billionaire media mogul will serve that year under house arrest or even by performing community service.

The high court also sent back another part of the conviction — a five-year ban from political office — to a Milan appellate court. Even if the appellate court decides that Berlusconi can't hold office, the Senate would have to vote to revoke his seat, setting up a potential showdown with the Constitutional Court. And if he is eventually removed from office, Berlusconi will still be able to head up his People of Liberty (PdL) party — as opposition leader Beppe Grillo leads his, even though he's ineligible to hold office.

Still, this is decidedly bad news for Berlusconi. After facing at least 20 corruption and other charges in his 20 years at the top of Italian politics, this is his first unappealable conviction. He's also fighting a seven-year jail sentence for having sex with a minor, related to his infamous "bunga-bunga" parties, and a conviction for illegal wire-tapping. And a ban from politics could have dire consequences for his media company, Mediaset.

"This signals another step towards the end of Berlusconi's political life," analyst Claudio Aspesi tells Reuters. "It will be increasingly difficult for him to govern, and this in turn basically means the political protection he has been able to give Mediaset in recent years is destined to wane."

An uncharacteristically grim Berlusconi railed against the ruling in a nine-minute video aired on his Rete4 channel (watch highlights above), calling the ruling "absolutely groundless," attacking the judiciary, saying he will revive the Forza Italia party that brought him to power in 1994, and playing the victim card:

"In exchange for the commitments I have made over almost 20 years in favor of my country and coming almost at the end of my public life, I receive as a reward accusations and a verdict that is founded on absolutely nothing, that takes away my personal freedoms and my political rights. That is how Italy recognizes the sacrifices and commitments of its best citizens? Is this the Italy that we love? Is this the Italy that we want? Absolutely not."

While the prognosis for Berlusconi's future is mixed, analysts are pretty unanimous that the ruling spells trouble for the fragile left-right coalition government headed by Prime Minister Enrico Letta and his Democratic Party (PD, the liberal part of the coalition). Giovanni Orsina at Rome's Luiss-Guido Carli University spells out three scenarios for CNBC:

A) That Berlusconi votes the government down and tries to have new elections. B) Berlusconi says that the government must not suffer from his personal problems, but the PD decides that they cannot go on in a coalition with a party led by a man convicted for tax fraud and we have new elections, or C) The government goes on, even though it is much weaker. [CNBC]

Orsina and most other observers are going with Option C for now, and the PdL says it will continue to support Letta's government for the time being. But there's a much better chance that Italy's government will, once again, collapse before Berlusconi ever sees the inside of a prison cell.