The EU's foreign policy chief has praised the "brave" leaders of Serbia and Kosovo for reaching a landmark deal to normalise ties.
"I wasn't sure we would get a deal until the moment the two prime ministers initialled it," Cathy Ashton said. "I really didn't know."
Baroness Ashton mediated 10 rounds of talks between Serbia's Ivica Dacic and Hashim Thaci of Kosovo.
Kosovo's Serbs have long refused to recognise the Kosovan government.
The deal, reached on Friday, does not mean Serbia recognises Kosovo as an independent state. But it does - in effect - concede that the government in Pristina has legal authority over the whole territory, including Serb-majority areas of northern Kosovo.
There are about 50,000 Serbs concentrated in about one-fifth of the territory. There has been sporadic violence between them and the ethnic Albanian majority since the 1999 conflict, when Kosovo broke away from Serbia.
The text of the agreement gives Kosovo Serbs their own police and justice representatives within the Kosovan system. It also makes it clear that some details have still to be finalised.
"Discussions on energy and telecoms will be intensified by the two sides," it says, "and completed by June 15".
Baroness Ashton is confident this will be done on schedule.
"I've heard the word historic," she told the BBC. "And maybe, looking back, that is how people will view it."
She hopes that in June EU member states will give a green light for formal EU membership negotiations with Serbia to begin, but she warns that implementing the deal with Kosovo will be a big challenge.
"I think it will be successful," she said, "but I think it will take time".
Other senior figures in European foreign policy agree.
"Implementation will not be easy but I think a Rubicon has been crossed," said the Swedish Foreign Minister Carl Bildt, a former UN and EU envoy in the Balkans. "There is no way back."
The agreement inevitably has its critics. The leader of the Serbian Orthodox Church, Patriarch Irinej, said it appears to "mark the pure surrender... of our most important territory in spiritual and historical terms."
"I'm sorry to hear those words," Baroness Ashton said.
"We've seen some demonstrations, but we've always said we need a big selling operation.
"People need to feel this is being done for them, not to them. It is their agreement."