Princess Alexa is one of the two main protagonists of the thirteenth Barbie full-length film Barbie & the Diamond Castle. She is a Princess Of Music who lives in a cottage in the woods with her best friend Liana. They find a magical mirror that houses a muse apprentice, Melody and hopes to help her find the magical instruments hidden inside the titular Diamond Castle and stop the fallen muse Lydia from destroying them.
She also has a necklace with a magical heart-shaped diamond from the Diamond Castle that she and liana found in the stream that was great their garden. It protects them both from Lydia's evil spells and enchantments.