Three of the most popular TV series from writer and director Joss Whedon are coming to Facebook.

All episodes of "Buffy the Vampire Slayer," "Angel," and "Firefly" will be available to stream on Facebook Watch, the company's section for series and other premium video content, starting on Friday. Viewers will be able to binge with others real-time using the platform's communal viewing capabilities, kicking off with three official Watch Parties on launch day.

The shows, which originally aired on TV around the turn of the millennium and will evoke nostalgia among older millennials, may reflect Watch's new strategy to focus on viewers in their 30s and older, as CNBC previously reported. Facebook Watch was meant to let the company tap into the digital video advertising industry, which was worth $28 billion in 2018 per eMarketer. But the service, which launched in August 2017, has yet to gain widespread household recognition, according to publishers and media buyers.

"Our focus with Facebook Watch is on content and experiences that help people connect, ignite conversation and build community," Facebook vice president of video Fidji Simo said in a blog post. "We think there is a range of content that can do this, and are excited to bring iconic pop culture favorites like these series for their avid fan communities to experience them in new ways, and for new fans to discover these awesome 90s classics."

The financial terms and duration of the deal were not disclosed.

The initiative is a critical part of Facebook's efforts to diversify its revenue beyond News Feed ads. The company is looking to expand video, messaging, and Stories to ensure future growth as other areas slow down, CEO Mark Zuckerberg said during a call with analysts in October. The company was expected to spend between $1 billion and $2 billion on video content through 2019, Variety reported.

Facebook has indicated to some publishers they plan on focusing the service to focus on older millennials, Gen X and up, which could also be a reaction to teens leaving the main Facebook platform.

Facebook is heading into shiny new territory with this deal, which marks some of the best-known series available on Facebook Watch. The company has been looking to acquire the rights to existing intellectual property (IP) for Watch, several video publishers have told CNBC. The company is creating a new version of MTV's "The Real World," for example. Other companies have posted their entire content library on Facebook Watch, including Freemantle and its global "Got Talent" series and some selections from FilmRise. A Facebook spokesperson said it will continue to focus on identifying content that will engage its community.