The jewel is thought to have been a gift given to her mother in 2014, when Lady Louise would have been just 11-years-old.
The necklace choice is poignant, not only because it had been worn for prominent royal occasions, but because it belonged to the Countess of Wessex.
Other social media users commented on the overall look and praised the teenage royal.
“She really is a lovely young woman,” wrote Twitter user ‘Edie Lorenzo’.