Princess Ievna was half telling the truth and half lying to the second prince of Breviel. She was telling the truth that Crown Prince Randver knew that she was no longer a normal human, but the Crown Prince did not know the details about the curse.
The Crown Prince didn't ask her that, and Princess Ievna thought that she could keep the secret for now. 'Maybe he doesn't even know I'll turn into a red rose after the sun goes down,' she thought, and maybe that could be an advantage for her.
She still remembered how the Crown Prince had confidently said that he already knew the secret, but the man didn't mention the red rose at all. The blonde man knew that she was cursed, but he didn't know what kind of curse was on her body to this day.