"Glee" Season 5, Episode 9, "Frenemies," is quite close to the FOX series' 100th episode. This landmark episode rivals only the Cory Monteith tribute in October as the biggest show of the series throughout its five years on air. Will Dianna Agron join the other original Gleek actors this time? Meanwhile, what songs will Lea Michele and Naya Rivera be singing in Glee 5x09? (Must-watch!)

Spoiler alert: This feature contains spoilers from the next new episode of Glee Season 5 (Episode 9) on the U.S. network FOX. Reports have surfaced on the song list, which includes something from "American Idol" alum Adam Lambert. The series returns on Feb. 25, back to its Tuesday time slot.

Glee creator Ryan Murphy himself announced Dianna Agron is returning to the show for its very special 100th episode. It will be recalled that Dianna's absence in "The Quarterback" (The Cory Monteith tribute) was riddled with controversy. It was rumoured that Lea Michele and Murphy have schemed to isolate Dianna from the tribute. Watch the video below to see how Dianna responded to a Lea-related question.

"Dianna is IN for Glee 100th!" Ryan Murphy announced on Twitter. To date, the tweet has gathered over 13 thousand "favourites" and almost the same number of "retweets." A tweet this well-received is considered viral on the social media site.

The 100th episode will be quite a reunion for the original cast of Glee. Heather Morris, Mark Salling, Amber Riley, and Harry Shum will also be returning alongside Dianna Agron, reports TV Line. For reference, Glee Season 5, Episode 9 is the series' 98th episode.

WATCH: 'Glee' 5x09 Teaser Video on YouTube (FOX)

Here is the rumoured Glee Season 5, Episode 9 song list in 'Frenemies,' according to Hypable:

- "Don't Rain On My Parade" - Santana Lopez (Naya Rivera) - original from the musical "Funny Girl"
- "I Believe In A Thing Called Love" - Kurt (Chris Colfer) and Elliott (Adam Lambert) - original by The Darkness
- "Whenever I Call You Friend" - Artie (Kevin McHale) & Tina (Jenna Ushkowitz) - original by Kenny Loggins
- "My Lovin'" (You're Never Gonna Get It) - Artie (Kevin McHale) & Tina (Jenna Ushkowitz) - original by En Vogue
- "Brave" - Rachel (Lea Michele) & Santana (Naya Rivera) - original by Sara Bareilles
- "Every Breath You Take" - Rachel & Santana - original by The Police
- "Breakaway" - Artie, Tina & Blaine (Darren Criss) - original by Kelly Clarkson

WATCH: Dianna Agron Talks About Friendship with Lea Michele

(Source: The Showbiz 411)

Based on the "leaked" song list, it seems Artie and Tina will have some nice moments together on Glee Season 5, Episode 9. Are they friends or romantically together in this episode? ("Whenever I Call You Friend" is just the right post-Valentine song, too!) Fans can also expect a Santana vs Rachel sing-off. Worth noting is that Sam (Chord Overstreet) and Rachel have no follow-up moments in the next episode. Their bonding in New York does hint some future complications. Fans should calendar the FOX air date for Glee 5x09: Feb. 25.

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