Karima el-Mahroug, a Moroccan who is now 20 and better known by her stage name “Ruby the Heartstealer,” was due to testify in the Milan court in December but failed to show up, telling her lawyer she was on holiday in Mexico.
“Karima will be present in the courtroom on Monday,” her lawyer Paola Boccardi told Reuters, adding that Mahroug had returned to Italy on Friday.
Berlusconi, 76, who is seeking a fifth term in government in a parliamentary election on Feb. 24-25, is accused of paying Mahroug for sex when she was under 18, which is the minimum legal age for prostitution in Italy.
The billionaire media mogul denies all charges and Mahroug has said she never had sex with him.
In December, a judge set Feb. 4 as the date for the final hearing in the trial, making a verdict possible before the election.
However, one of his Berlusconi's lawyers said he was considering asking for the trial to be suspended until after the election.
A poll by the SWG company published on Jan. 11 put the center-left about 10 points ahead of Berlusconi's center-right.
The trial, in which dozens of aspiring showgirls have described so-called “Bunga Bunga” parties at Berlusconi's residences, is the most sensational of his legal cases and has received huge media attention in Italy and abroad.
Berlusconi is also accused of abusing his powers when he was still prime minister to have Mahroug released from police custody when she was briefly held over theft allegations.
Berlusconi could be sentenced to up to 15 years in prison, but he would not serve time unless he also lost the two appeals allowed by Italian law, usually a lengthy process.
Berlusconi, who controls Italy's biggest private broadcaster Mediaset, was driven from office as prime minister in 2011 at the height of the financial crisis.
His People of Freedom party backed the technocrat government of Mario Monti for a year before bringing it down by withdrawing its support last month.