Cher as Meryl Streep's mom in Mamma Mia 2: Hollywood's eyebrow-raising history of implausible casting

Hollywood A-listers Meryl Streep, Pierce Brosnan and Colin Firth returned to the big screen this week in Mamma Mia! Here We Go Again, but there's another star in the mix that could overshadow them all.

The glitzy follow-up to 2008's Mamma Mia features legendary singer and actress Cher as grandmother to Sophie, played by Amanda Seyfried — and mother to Donna, played by Streep. 

Given that Cher is just three years older than Streep, the casting choice has left some viewers perplexed.

Laura Bradley, a staff writer for Vanity Fair, told Day 6 that she's willing to suspend her disbelief in Mamma Mia! Here We Go Again. But as she pointed out, it's not the first time Hollywood has done this.

Here's what she had to say about some of the industry's biggest age-related gaffes.

Alexander (2004)

When it comes to discrepancies in age casting, Bradley said she tends to be more forgiving in comedies.

But in the 2004 drama Alexander, she had a harder time reconciling the one-year age difference between Angelina Jolie and Colin Farrell, who played Jolie's son.

"I think in her case in particular, she was cast because of her sex appeal and the sexual tension between the two characters was played up," she said.

"Obviously, that is an exception to the normal rule, because we don't normally want a mother with flat-out sexual tension with her son. But in general across Hollywood, I think there's often a reluctance to hire actresses who actually either look their age or look the age of the person that they're actually supposed to play. "

Star Trek (2009)

Bradley said she understands that science fiction movies tend to bend the rules of reality, so she's willing to be somewhat lenient when it comes to implausible age differences between actors.

But in 2009's Star Trek, she said she found it strange that Winona Ryder played the mother of Spock, Zachary Quinto's character. Ryder is only six years older than Quinto.

"I remember they gave her some grey highlights and a little bit of old age makeup," Bradley said.

"I think Winona Ryder is somebody who kind of transcends time as far as Hollywood is concerned. But even for me, that was pretty dubious."

Brokeback Mountain (2005)

Another film whose casting choices seemed "egregious" to Bradley was Brokeback Mountain. In the film, Heath Ledger played the father of Kate Mara, who was only four years younger than he was.

But despite the closeness in age, Bradley acknowledged that the casting was remarkable in another way — because Hollywood rarely casts a man to play a young father.

"What you normally see [is] mothers who are implausibly young, not fathers. So hats off to them I guess for that."

What were some good casting decisions in Hollywood?

Bradley said she is more willing to look past awkward age differences in comedies, because they can be played to comedic effect.

She pointed to the 2004 film Mean Girls as a classic example. Amy Poehler, who played the mother of Rachel McAdams' character, was only seven years older than her onscreen daughter.

"When you look at a film like that where Regina George, Rachel McAdams' character, her mother is sort of a woman who tries to exist in a state younger than she really is. She's trying to be one of the girls," Bradley said.

"It almost makes sense to have someone a little too young to be the mom playing her."

As for why the casting of Cher as Streep's mother doesn't bother her, Bradley said when she first saw the casting announcement, her only reaction was "unmitigated joy."

She added the casting department made "the perfect choice regardless of age."

"Cher herself kind of exists independent of age," she said.

"I'm pretty sure that she's going to be singing and dancing and starring in films playing people's grandmothers and great-grandmothers until we are all in the ground."

This interview has been edited for length and clarity. To hear more from Laura Bradley, download our podcast or click the 'Listen' button at the top of this page.