The actress decided to surprise six-year-old Avery Huffman with the recorded call after learning the girl had been diagnosed with an inoperable brain tumour, called diffuse intrinsic pontine glioma (DIPG), last month (Jun15).

Bell reached out to the Huffmans through a mutual friend and got back into character to share a surprise honour with little Avery.

In the message, the mother-of-two praises Avery for being "so brave" and names her an honorary Princess of Arendelle. She ends the call by claiming she had to leave to "go build a snowman with Olaf".

Her dad, Brandon, has since shared video footage of Avery listening to the voicemail on his blog.