La Bella Principessa, a recently authenticated work of Leonardo Da Vinci, possesses an enigmatic smile similar to that of the famous Mona Lisa, proving a technique used by the great artist in capturing the deep thoughts of his subjects in his artwork.

Researchers Alessandro Soranzo and Michelle Newberry examined the La Bella Principessa and found that her smile seemed to change depending on the distance and angle from which it is viewed, according to Scientific American.

Using a series of psychophysics experiments, the researchers observed that "a perceived change in the slant of the La Bella Principessa's mouth influences her expression of contentment," creating an illusion that they refer to as the "uncatchable smile." This illusion, the researchers say, is the same technique used in painting the Mona Lisa, which Da Vinci created after La Bella Principessa.

"The results from the experiments support the hypothesis that that there is a gaze-dependent illusory effect in the portrait of La Bella Principessa," Soranzo said in a press release published online by the Sheffield Hallam University.

Simply put, the smile appears to change depending on the angle you view the portrait from.

La Bella Principessa is believed to be the portrait of Bianca Sforza, daughter of Ludovico Sforza, who was a duke of Milan. It is said to have been drawn a few months before the young girl married Galeazzo Sanseverino, commander of the Milanese forces and a known Da Vinci patron, whom she wed when she was 13 or 14-years-old, according to National Geographic.

What made the portrait stand out as a Da Vinci artwork was the pensive expression on the girl's face, which displayed the "motion of the mind," a common denominator in Da Vinci's works.

"With his knowledge of the turbulence surrounding the Court of Milan at that time, Leonardo would have been aware of inner tensions between the fresh innocence of a young girl on the threshold of womanhood and her impending marriage and courtly destiny," Michael Pickard from the University of Sunderland said in the press release.

The question in many people's minds is: Was the illusory technique displayed in La Bella Principessa and Mona Lisa intentional?

"Given Leonardo's mastery of the technique and its subsequent use in the Mona Lisa, it is quite conceivable that the ambiguity of the effect was intentional, based on explicit artistic skill and used in line with Leonardo's maxim that portraits should reflect some 'inner turmoil of the mind,'" Soranzo said.

The research was published online on June 4 in the journal Vision Research.