In response to the evolving geopolitical landscape and security concerns in Southeast Europe, Croatia, Albania, and Kosovo have strengthened their defence cooperation by signing a trilateral declaration in Tirana.
Edit (March 22nd, 2025): Due to the public interest the full text of declaration has been released.
It has been hypothesised that Bulgaria could join and this is seen as a hostility by Serbia
https://novinite.com/view_news.php?id=231382
However, winds and governments are changing way too often in Bulgaria and foreign policy is completely unpredictable. The only constant is that it’s toothless.