Michelle Trachtenberg was reportedly in talks for the 'Buffy the Vampire Slayer' revival before her death

A source told DailyMail.com: "Michelle Trachtenberg was in talks to return to Buffy the reboot and she was incredibly hopeful about it."

Trachtenberg joined the series for its fifth season as Dawn Summers, and she remained on the show until its conclusion with season seven in 2003.

It's said Sarah was keen to bring her back for the highly anticipated sequel series as "the reboot would need her as much as it needed Sarah".

The insider added: "It is still in early stages, but the reboot will feel her void.

"Fans were hopeful that she would be cast and Michelle expressed interest and excitement at the opportunity."

The New York Police Department (NYPD) has confirmed to PEOPLE that it responded to a 911 call at 1 Columbus Place in New York City.

The NYPD added: "Upon arrival, officers observed a 39-year-old female unconscious and unresponsive.

"EMS responded to the location and pronounced the victim deceased. Criminality is not suspected."

Sarah is yet to comment on Trachtenberg's death.

20th Television - which is the studio behind the upcoming 'Buffy' reboot - shared in a statement to PEOPLE magazine: "Michelle touched a generation of television fans throughout her career, including in her unforgettable role as the independent and strong-willed Dawn Summers in 'Buffy'.

"She brought depth, heart, and authenticity to every performance and will be remembered for her remarkable talent.

"Our sincere condolences go out to her family and friends - she will be deeply missed."

And Alyson Hannigan, who played Willow Rosenberg on the classic vampire drama, has paid tribute to her late co-star.

She wrote on Instagram: "I am deeply saddened by the news of Michelle's passing.

"She brought a loving energy to the set of Buffy. My thoughts are with Michelle's family and friends."