Viewers have been shattered to learn the most recent House of the Dragon episode was a breakout star's last.

Australian actress Milly Alcock, 22, won the hearts of diehard Game of Thrones fans as the younger version of Princess Rhaenyra Targaryen, who is played by British actor Emma D'Arcy, 30, in the final five episodes.

After the fifth episode aired on Foxtel and Binge on Monday, viewers took to Twitter in droves to express their devastation Alcock would no longer appear.

Alcock's starring role in the big-budget HBO prequel marked her major transition from local projects to shows with global reach.

Before her big break, the Sydney-born actress starred in the critically acclaimed 2019 Foxtel series Upright opposite comedian Tim Minchin, in which she played the loveable, rebellious teenager, Meg.

Thankfully for fans of Alcock and Upright, she's already finished filming season two of the series, which was shot in Queensland this year and will feature eight episodes.

Foxtel executive director of television Brian Walsh said he was thrilled Alcock was rejoining the series amid her rise to international superstardom.

Milly Alcock as young Rhaenyra Targaryen and Emily Carey as young Alicent Hightower in The House of the Dragon. Photo / HBO

"Tim Minchin's Upright was a smash hit for Foxtel and a subsequent breakout success when it was brought to Binge audiences last summer.

"The series is uniquely Australian, brash and bold, full of fun and great heart. The story of Lucky [Minchin] and Meg, and their unexpected journey across the Nullarbor, won fans of all ages – and we're set to take off once again on a memorable road trip with unexpected consequences."

• Steve Newall: If you like dragons & politics, you'll love House of the Dragon

Alcock told the Sydney Morning Herald she pulled the pin on studying her diploma to accept her role in Upright a few short years ago.

"School's never been for me. I've never been somebody who's thrived in the school environment," she told the publication.

Milly Alcock won the hearts of viewers as Young Rhaenyra. Photo / HBO

"There's a stigmatisation of people who drop out of high school. But I couldn't turn down Upright for a piece of paper. That just seemed ridiculous to me and infuriating."

Sometime between the end of filming Upright and landing the role in House of the Dragon, Alcock was washing dishes and living in her mother's attic.

And now, the world is at her feet.

"I never thought this would happen to me," Alcock told Stellar.

"This doesn't happen to people like me, so it was incredibly quick."