It was during the night from 25 to 26 October that Yugoslav soldiers boarded the last ship sailing under the Yugoslav flag from the port of Koper, the withdrawal considered one of the final steps in Slovenia's independence efforts.
After Slovenia declared independence on 26 June, a ten-day war broke out when the Yugoslav army attacked it from the barracks on the Slovenian territory on 27 June.
The war was followed by talks which resulted in Slovenia agreeing to a three-month moratorium on independence implementation as part of what is known as the Brijuni Declaration.
As the moratorium was about to expire, Yugoslavia's authorities realised it would be impossible to keep Slovenia in the federation.
Preparations thus started for the army's pull-out from Slovenian territory.
Two independence figures, General Ladislav Lipič and Dimitrij Rupel, believe that with the departure of Yugoslav troops, Slovenia claimed full military and general sovereignty, which it has largely retained despite joining the EU and NATO.
Former Foreign Minister Rupel thinks three things made the departure easier: the Brijuni Declaration, an improvement in relations between Slovenia and Serbia in the summer of 1991, and Serbia's authorities being no longer able to count on Soviet support as the USSR broke up.
"After that, it was all much easier and painless," said Rupel, who is convinced Slovenia is still a sovereign country, "and I hope it remain so for quite some time".
What bothers him is that some perceive independent Slovenia as a continuation of the former undemocratic Yugoslavia and that the differences between the two are not being highlighted strongly enough.
"In 1991, we shook off socialism and Yugoslavia, and it was then that our state was formed, not on 9 May 1945, as some would like to make us believe," he told the STA.
The holiday will be marked today with a national ceremony in Celje organised by the Association of Slovenian Independence War Veterans and the Sever Police Veterans' Association, and addressed by Prime Minister Marjan Šarec.
However, the Association for the Values of Slovenian Independence, which was set up by conservative independence figures as an ideological counterweight to the Association of Slovenian Independence War Veterans, organised its own ceremony last night, followed by mass at the local church.
Observed for the first time in 2015 after it was designated a holiday earlier that year, Sovereignty Day is one of the newest Slovenian public holidays.
You can watch a BBC documentary on the birth of Slovenia here