Not a real palace in the royal sense, but the PALACE OF SERBIA houses several ministries and cabinet-level agencies. A true 65,000 square meter showplace completed in 1959. Of course it was first called The Palace of the Federation (i.e. Yugoslavia).
I had the privileged opportnity yesterday of touring the building, and with its art and restored furniture from various parts of the former Yugoslavia, it was literally mind-blowing. If the opportunity arises again, I may go back.
What you see in the photo here behind those closed doors is Tito's (RIP) office, but we were not allowed in.