Glee's 2-part series finale to feature footage of Cory Monteith

The first hour of the song-and-dance smash hit Glee's two-part finale is set to air tonight after a six-year series run, and the emotional chapter will include footage of the late Canadian TV star Cory Monteith.

The episode was screened last week for a private audience in New York at a panel attended by some of the series' biggest stars, including Lea Michele.

Entitled 2009, the episode focuses on how New Directions, the name of the glee club, came together and evolved in its earliest days. It will air at 8 p.m. ET.

According to Entertainment Weekly, footage of Monteith is "sparingly" integrated into the episode to represent a time when the rest of the would-be New Directions members were still unsure whether Monteith's character, quarterback Finn Hudson, is just another hard-headed jock at the fictional William McKinley High School. 

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Monteith, one of the show's breakout stars, died of an accidental overdose at a posh Vancouver hotel in July 2013, between the fourth and fifth seasons. During season five, Monteith's character was written out of the show with an off-screen death and he was honoured during an emotional farewell episode, aired in October of that year.

At the New York panel discussion, Lea Michele told the audience that after the series wrapped filming, the entire cast broke down and spent time together crying. 

"That was the day I fell to my knees and cried. I literally had to call my mother to come," she told Entertainment Weekly. 

While the popularity of the show waned slightly in later seasons, Glee leaves behind a remarkable legacy.

First of all, it dared to try something that had seldom if ever worked on series television: mix episodic narrative with musical production numbers. It set those performances in the context of a show choir at a fictional high school, ​a setting replete with stories about growing up, self-acceptance, perseverance and dreams.

Legacy of tolerance

Glee did something else few would have thought possible: it helped make glee clubs cool.

And it served as a platform for new talent, launching stars like Lea Michele and Monteith while giving wide exposure to veterans like Matthew Morrison and Jane Lynch, with guest appearances by a broad range of celebrities that included Helen Mirren, Lindsey Lohan and Ricky Martin.

Pop music — both new and well-established — reached new audiences, both on the show and through sales of more than 50 million songs and 13 million albums under the Glee brand.

While it was demonstrating a viewer appetite for musical theatre among its audience, Glee accomplished one more thing: it highlighted, and even helped normalize, young people traditionally deemed marginal both in real life and on TV. Among the characters included in the Glee big tent was transgender girl Wade "Unique" Adams. Tolerance, or at least reaching for it, was a Glee hallmark.