(ANSA) - BELGRADE, APR 22 - Slovenia commemorates 20 years since its entry into the European Union with a ceremony at Brdo Castle near Ljubljana. Italy's President of the Republic, Sergio Mattarella, is present. The President of the Republic of Slovenia, Natasa Pirc Musar, has invited the presidents of all neighbouring countries to participate in the summit. Austrian President Alexander Van der Bellen, Croatian Zoran Milanovic, and Hungarian Tamas Sulyok are all expected. (ANSA).