Viola Margaret Jane Prettejohn (born July 2003) is a British actress. She is known for her role as Myrtle Haplisch in the HBO series The Nevers (2021–2023). She played young Princess Elizabeth in the sixth season of The Crown (2023) on Netflix.

Prettejohn made her television debut in the second season of the Starz series Counterpart as a young version of Olivia Williams' character Emily.

In August 2019, Prettejohn joined the cast of the Joss Whedon series The Nevers on HBO as Myrtle Hapslich.That year, she was also played Fake Ciri in the Netflix television series The Witcher.

In 2023, Prettejohn played a teenage Princess Elizabeth on series six of The Crown in flashback scenes set on Victory in Europe Day alongside Beau Gadsdon as young Princess Margaret. In so doing, she became the fifth actress after Claire Foy, Olivia Colman, Imelda Staunton, and Verity Russell to play Elizabeth on the series. That year, she filmed the role of Finn in Ben Wheatley zombie-satire Generation Z for Channel 4.

She has an upcoming role in the BBC One adaptation of Hilary Mantel's Wolf Hall: The Mirror and the Light as Mary FitzRoy, Duchess of Richmond and Somerset.