Updated: Mackenzie Foy has officially signed on to star in Breaking Dawn. See below for details.

The cast of The Twilight Saga: Breaking Dawn – the two-part finale to the successful franchise – is continuing to grow with the likes of Rami Malek and Lee Pace recently joining established franchise stars Kristen Stewart, Robert Pattinson and Taylor Lautner.

Today we’re hearing word of not one but two new additions to the Breaking Dawn cast in the form of Maggie Grace (Lost, Taken) and newcomer Mackenzie Foy (Flashforward, ‘Till Death). The pair will play a foe and friend (respectively) of Stewart’s character, Bella Swan.

First up we have Grace, who is confirmed to have joined Breaking Dawn‘s extensive cast. She will play Irina, “a member of the Denali coven, considered cousins to the Cullen clan as the only other “vegetarian” vampire group.” Fans of the Breaking Dawn book will know that, “when Irina blames the Cullens for the death of her lover, her actions set in motion a terrifying chain of events.”

Grace is making a great career for herself, with Lost officially putting her on the map. She’d acted in a few things before that but nothing that gave her the exposure that Lost did. Her first big role post-Lost was in the Liam Neeson thriller Taken (playing Neeson’s kidnapped daughter) and she has several more projects in the works, including the Dwayne Johnson action film Faster and a possible sequel to Taken. With her casting in Twilight she can now rest assured she has one of the most popular movie franchises of recent years on her résumé.

The second actress joining Breaking Dawn is 9-year-old Mackenzie Foy who, according to Entertainment Weekly, is “inches away” from signing on to play, [SPOILER ALERT!] “Renesmee, Edward and Bella’s vampire/human love child.”

Questions have arisen about how Foy will play the character, who ages ’17 years in the space of just seven.’ Some sources are speculating that director Bill Condon could employ similar technology used in The Curious Case of Benjamin Button to digitally make Foy look younger/older.

Wouldn’t it be easier to get several actresses to play Renesmee at different ages? Just a suggestion.

Summit Entertainment and the filmmakers behind Breaking Dawn are remaining secretive about how they plan to have Foy play the character at different ages, but with The Twilight Saga‘s rabid following, I’m sure it won’t stay a secret for very long :-P .

Update: Twilight author Stephanie Meyer announced on Facebook that Mackenzie Foy has officially signed on to star as Renesmee in Breaking Dawn after being “inches away” from joining the cast. Meyer had this to say about the 9-year-old newcomer:

“Very excited about our new Renesmee, Mackenzie Foy… She’s an amazing young actress and I’m excited to work with her.”

It’s still unclear how exactly Summit is going to age Foy the amount that she does in the story but it’s still speculated that similar technology to that used in The Curious Case of Benjamin Button will be utilized, as well as other younger and older actresses maybe being hired.

The two-part Breaking Dawn epic is being written by Twilight franchise scribe Melissa Rosenberg, with the series switching up directors once again from Eclipse‘s David Slade to Bill Condon (Dreamgirls). With the fourth book apparently being a bit more adult than the previous three, I’m hoping for that tone to be transferred faithfully to the big-screen (as much as the PG-13 rating allows).

Part 1 of The Twilight Saga: Breaking Dawn will be released (maybe in 3D, maybe not) on November 18th, 2011 with Part 2 following almost exactly a year later on November 16th, 2012.

Source: Deadline and Entertainment Weekly (Image source: Dani Brubaker)