The Short Version
Multiple high-authority, independent news sources — including AP News, Radio Free Europe/Radio Liberty, and Al Jazeera — confirm that Boyko Borisov was detained in March 2022 during a formal EU prosecutor-led corruption probe and has faced recurring corruption allegations throughout his political career. While no formal charges resulted from the 2022 detention, the claim's threshold of "credible allegations or formal investigations" is clearly and directly met by the documented evidence. Partisan denials from Borisov's own party carry no independent evidentiary weight.