MILAN, May 18 (Reuters) - Italian billionaire Leonardo Del Vecchio has further raised his stake in Mediobanca after the Berlusconi family said this week it had liquidated its holding in the Milanese merchant bank.

Del Vecchio, founder of Ray-Ban owner Luxottica, rocked Italy's financial establishment in 2019 by emerging as the biggest investor in Mediobanca, just as a core of its long-term shareholders unravelled.

A regulatory filing on Tuesday showed Del Vecchio, 85, held 15.402% of Mediobanca as of Monday through his holding company Delfin, up from 13.17% previously.

Del Vecchio has been steadily increasing his stake and has secured European Central Bank approval to get to just under 20%.

Fininvest, former Italian Prime Minister Silvio Berlusconi's holding company, said on Monday it had sold its 2% Mediobanca stake for 174 million euros ($212 million).

A source close to the matter said the stake had been sold at 9.814 euros a share, which was in line with the carry value of the holding on Fininvest's books.

Fininvest first acquired 1% of Mediobanca in 2007, before doubling the size of its holding the following year.

Shares in Mediobanca are at their highest level since the start of 2020, having doubled in value over the past 12 months, outperforming a 73% rise in Italian banks.

They closed 0.9% higher at 9.87 euros on Tuesday, outperforming Milan's blue-chip index.

Del Vecchio's investment in Mediobanca has raised questions over his strategy for both the bank and insurer Generali, in which Mediobanca is the biggest shareholder with a 13% stake.

He is also the third-largest shareholder in Generali, behind fellow Italian magnate Francesco Gaetano Caltagirone.

Following in Del Vecchio's tracks, Caltagirone in March also decided to take a stake in Mediobanca. ($1 = 0.8189 euros) (Reporting by Claudia Cristoferi; Writing by Valentina Za; Editing by Alexander Smith)