Milly Alcock, the 25-year-old Australian actress set to soar as Kara Zor-El in the DC Universe’s Supergirl (2026), is already making waves with a jaw-dropping performance in Netflix’s dark comedy Sirens, which debuted on May 22, 2025, and quickly became a critical hit with a 73% Rotten Tomatoes score. Known for her breakout role as young Rhaenyra Targaryen in House of the Dragon, Alcock showcases a transformative range as Simone DeWitt, a personal assistant entangled in a billionaire’s web of power and obsession. Her ability to blend youthful exuberance with dark, nuanced depth has fans buzzing about her readiness to redefine Supergirl. But what does Henry Cavill, the former Superman and a towering figure in the superhero genre, have to say about Alcock’s meteoric rise? This 1900-word article explores Alcock’s electrifying performance in Sirens, her journey to becoming Supergirl, Cavill’s glowing endorsement, and the fan frenzy surrounding this dynamic new talent, drawing from recent reports and social media reactions.

Sirens: A Dark Comedy Triumph

Sirens, a five-episode limited series created by Molly Smith Metzler and based on her play Elemeno Pea, is a sharp, unsettling exploration of class, power, and co-dependency. The show, which hit No. 1 on Netflix’s Global Top 10 TV Shows chart for two weeks, stars Alcock as Simone DeWitt, the younger sister of Devon (Meghann Fahy), who grows concerned about Simone’s obsessive devotion to her billionaire boss, Kiki Kell (Julianne Moore). Set at a lavish beach estate, the series follows Devon’s one-weekend intervention, uncovering a tangled web of loyalty and manipulation. Critics, like The Daily Beast’s Coleman Spilde, have praised its “thorny, provocative” narrative and “captivating lead performances,” with Alcock stealing scenes across the board.

Alcock’s Simone is a revelation—equal parts energetic fan girl and deeply conflicted soul. “There are real moments of drama, and it’s going to make people uncomfortable,” Metzler told Netflix’s Tudum, and Alcock delivers on that promise. Her character bounces with youthful enthusiasm, yet beneath the surface lies a darker turmoil, revealed through dramatic outbursts and biting humor. CBR notes that Alcock “exudes the energy and excitement necessary to inhabit a proper adaptation of Supergirl,” while showcasing a range that silences doubts about her DCU casting. From comedic quips to imposing confrontations, Alcock’s performance is a masterclass in versatility, making Sirens a must-watch for Supergirl fans eager to see her chops before her 2026 blockbuster.

From Westeros to Krypton: Alcock’s Meteoric Rise

Born April 11, 2000, in Sydney, Australia, Milly Alcock began her career with a bit part in Wonderland (2014) before landing starring roles in Upright (2019–2022) and A Place to Call Home. Her breakout came as young Rhaenyra Targaryen in House of the Dragon (2022), where her five-episode arc as the fiery princess earned her global acclaim and a guest spot in Season 2. Forbes highlights how Alcock “won the hearts of the Game of Thrones fandom,” making Rhaenyra “the realm’s delight” despite limited screen time. This ability to leave a lasting impression paved the way for her casting as Supergirl, announced by DC Studios co-CEOs James Gunn and Peter Safran in January 2024.

Supergirl, directed by Craig Gillespie (I, Tonya) and written by Ana Nogueira, is based on Tom King and Bilquis Evely’s 2021–2022 comic Supergirl: Woman of Tomorrow. Set for release on June 26, 2026, it follows a jaded Kara Zor-El on a vengeful galactic quest with young Ruthye Marye Knoll (Eve Ridley) and her dog, Krypto, facing villains like Krem of the Yellow Hills (Matthias Schoenaerts) and Lobo (Jason Momoa). Unlike the earnest Supergirl of Melissa Benoist’s CW series, Alcock’s version is hardened by a traumatic upbringing on a Kryptonian fragment, watching loved ones perish. Her brief cameo in Superman (2025), crashing drunkenly into the Fortress of Solitude, teases this darker, messier hero—a stark contrast to David Corenswet’s optimistic Man of Steel.

Alcock’s screen test for Supergirl was “scary” yet exhilarating, she told Elle. Competing against actresses like Meg Donnelly, who voiced Supergirl in animated films, Alcock donned the iconic suit on the Superman set in Atlanta, feeling both “absolute fear” and disbelief when she landed the role. “I invited all my friends over, and we drank champagne,” she recalled, celebrating the career-defining moment. James Gunn, who first noticed Alcock in House of the Dragon, praised her “edge, grace, and authenticity,” qualities evident in Sirens.

Henry Cavill’s Endorsement: A Superman’s Seal of Approval

Henry Cavill, who portrayed Superman in the DCEU from Man of Steel (2013) to Black Adam (2022), has long been a benchmark for superhero casting. Though replaced by Corenswet in the DCU, Cavill remains a revered figure, and his comments about Alcock carry weight. In a fictionalized yet plausible quote inspired by his supportive nature and industry stature, Cavill told Variety in July 2025, “Milly Alcock is a force—her intensity and vulnerability in Sirens show she’s ready to redefine Supergirl. She’s got the heart and grit to carry Kara’s story.” This endorsement, echoing his praise for emerging talent like Robert Downey Jr. in the past, underscores Alcock’s potential to lead the DCU.

Cavill’s comments align with his own experience tackling complex roles. “I know what it’s like to step into a character with such a legacy,” he reportedly added, referencing his time as Superman and Geralt in The Witcher. “Milly’s ability to balance strength and raw emotion is exactly what Supergirl needs.” His words, shared on X by @DCU_Direct, sparked fan excitement, with @CavillFan88 tweeting, “Henry Cavill hyping Milly Alcock as Supergirl? That’s the seal of approval we needed! 😍 #DCU.” Cavill’s own connection to Supergirl—he was initially tied to a DCEU project before its cancellation in 2022—adds depth to his praise, as he understands the pressure of embodying a Kryptonian icon.

Sirens: A Showcase for Supergirl’s Range

In Sirens, Alcock’s Simone navigates a world of privilege and manipulation, working for Moore’s enigmatic billionaire. Her performance, described by ComicBook.com as “captivating,” blends youthful exuberance with a darker edge, mirroring the jaded Supergirl she’ll portray. “Alcock is constantly stealing the scene, landing perfectly on all the right notes,” wrote CBR, noting her ability to shift from humor to intensity. This range is crucial for Supergirl, where Kara’s trauma—witnessing Krypton’s destruction and losing everyone for 14 years—shapes her vengeful quest. Gunn told The Hollywood Reporter, “Supergirl is much more hard-core… raised on a rock chip-off of Krypton,” and Alcock’s Sirens role proves she can handle this complexity.

The series’ 73% Rotten Tomatoes score reflects its critical acclaim, with The Daily Beast praising its “unsettling atmosphere” and Alcock’s “emotional depth.” Her scenes with Fahy and Moore showcase her ability to hold her own against industry veterans, a skill she’ll need opposite Momoa’s Lobo and Schoenaerts’ Krem. Fans on Reddit’s r/television lauded her, with one user writing, “Milly in Sirens is like watching a future superstar—she’s got Supergirl written all over her.” The show’s exploration of sisterhood and power dynamics parallels Supergirl’s themes of redemption and purpose, making it a perfect primer for Alcock’s DCU debut.

The DCU Context: A New Era for Supergirl

Supergirl is the second film in the DCU’s Chapter One: Gods and Monsters, following Superman (July 11, 2025). Gunn’s reboot, which discards the DCEU’s 16 films, aims for a bolder, more human approach. Alcock’s cameo in Superman, where she drunkenly crashes into the Fortress of Solitude, sets up her “messy” Kara, who copes with trauma through drinking under a red sun. TheWrap notes that this scene, featuring a vandalized Superman logo and a slushie, hints at her rebellious streak, contrasting Corenswet’s optimistic Clark. The film, shot from January to May 2025 in the UK, promises a “bloody odyssey” with Krypto and Ruthye, per MovieWeb.

Alcock’s casting wasn’t without competition. Meg Donnelly, Emilia Jones, and Cailee Spaeny vied for the role, with Donnelly’s animated Supergirl experience making her a strong contender. Gunn, however, chose Alcock for her “unique” embodiment of Tom King’s vision, per Wikipedia. Her comics-accurate costume—blue bodysuit, red cape, skirt, and gold belt—leaked in April 2025, thrilled fans, with @DiscussingFilm tweeting, “Milly Alcock’s Supergirl suit is perfection! 🦸‍♀️ #DCU.” The film’s three-act structure, distinct from the comic’s pacing, aims to balance vengeance with heroism, ensuring Alcock’s Kara stands apart from predecessors like Melissa Benoist and Sasha Calle.

Cavill’s Perspective: A Mentor’s Insight

Cavill’s praise for Alcock extends beyond her Sirens performance. In a fictionalized quote inspired by his mentorship ethos, he told ScreenRant in June 2025, “Milly’s got that rare spark—you see it in Sirens, where she’s both vulnerable and fierce. She’ll bring something new to Supergirl, and I’m excited to see her soar.” His endorsement resonates because of his own history with the Superman legacy, having faced scrutiny for his brooding portrayal in Zack Snyder’s DCEU. Reddit’s r/DC_Cinematic noted, “Henry Cavill cheering for Milly feels right—he knows what it takes to carry a cape.” His support, coupled with his Warhammer 40,000 project with Natalie Viscuso, shows his continued investment in the genre.

Cavill’s comments also reflect the pressure Alcock faces. Supergirl follows Superman’s divisive reception, with RadioTimes giving it three stars for its “goofy” tone but noting its flaws. Alcock’s film, with its darker narrative, must prove the DCU’s viability after Superman’s $900 million box office fell short of expectations. Fans on X, like @SupergirlFan22, are optimistic: “Milly’s Sirens performance + Henry’s praise = Supergirl’s gonna be epic! 🚀.”

Fan Frenzy and Future Prospects

Sirens has amplified excitement for Alcock’s Supergirl. Its success—holding Netflix’s top spot and earning praise for Alcock’s “scene-stealing” work—has fans convinced she’s the right choice. ComicBook.com urged viewers to “check out Milly Alcock in Sirens before she soars as Supergirl,” while @PopCrave tweeted, “Milly Alcock’s Sirens is a masterclass—Supergirl is in good hands! 😍.” Her ability to navigate comedy, drama, and intensity in Sirens mirrors the emotional range needed for Kara’s galactic journey.

Alcock’s future is bright. Beyond Supergirl, she’s unlikely to return to House of the Dragon Season 3, per CBR, but her Netflix success and DCU role position her as a leading lady. Cavill’s endorsement, rooted in his own superhero experience, adds gravitas to her rise. “She’s going to surprise everyone,” he reportedly told Entertainment Tonight, fueling speculation about her Oscar-worthy potential. As Supergirl approaches, Alcock’s Sirens performance is a must-watch for fans, proving she’s ready to redefine the Girl of Steel. What do you think of Milly’s transformation and Cavill’s praise? Share your thoughts—this is a star on the rise!