Romans_Revenge:
It’s because those fans are now claiming her birthmark disappears when the serpent is with her ????
In the novel, XY sometimes concealed her identity when she went out in public and didn't want to be identified as the Princess of Gao Xing. That included some of the times when she went on outings with FFB in public (especially for certain activities, like visiting dance halls).
In the drama, rather than having her wear a veiled hat in those scenes, it seems that the production decided to have her hide the "birthmark" (as Tina mentioned, the temporary mark created by the Face Forming Flower that her mother and the King of Haoling planted in her, which gives away her identity as the Princess of Haoling).
Edit: Her outings with FFB in episode 22 and episode 23 are two examples. In episode 22, her birthmark is already hidden before she encounters FFB (when she goes to the Tushan delivery shop to have her next shipment of poisons delivered to XL).
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Chapter 16:
They practiced until mid-afternoon before Xiao Yao put her bow away.
The two of them did what they always did and went back to Xuan Yuan Castle to have lunch at a dance hall and take a nap.
The two of them rode alongside each other down the streets of Xuan Yuan, and despite Xiao Yao wearing a veiled hat, she was riding a winged horse. Plus Fang Feng Bei was beside her and the smart folks easily guessed she was the Princess. People got excited and pointed at her and crowds started gathering.
Xiao Yao was distracted this morning and grabbed the wrong winged horse. This one was encrusted with the gold emblem of the royal family and was likely a horse that pulled the Yellow Emperor’s carriage.
At this time, they were the only people moving on the street which felt totally strange but Xiao Yao had no choice but to put on her best haughty Princess impersonation as she and Fang Feng Bei passed.
Fang Feng Bei laughed. “I may be shameless but taking you to a dance hall in broad daylight in public makes even me feel sheepish.”
Xiao Yao laughed. “That means you’re not shameless enough and need to keep working on it.” Actually she didn’t have the guts either, worried that it’ll spread back to Gao Xing and her dad would hear of it.
Xiao Yao said, “Let’s go to Zhuan Xu’s place. He should be in Cao Yun Court until after dinner.”