The difference between Prince Alistair and Prince Silas in King Cyrus's eyes was jarring. While Prince Silas was kept by his twin sister, Prince Alistair was kept in two separate vaults hidden deep within Reaweth's dungeons. While his head was somewhere easily visitable due to the need for interrogation and the like, his body was kept in a maximum security cell which needed King Cyrus's authorization to access.
That meant that there was no way Atticus could access the body without having the Reawethen king's prior approval.
"Well done," King Cyrus commended, applauding joyously as he watched Prince Silas beam at him from his sister's side.
Check out the prequel: The Hidden King's Stolen Wife