January Jones’ X-Men Costars: She’ll Be a Great Mom!

 Gary Gershoff/WireImage.com

At Wednesday night's X-Men: First Class premiere in NYC, the action flick's cast was gushing over their co-star, January Jones,' pregnancy.

"It's great!" Rose Byrne told Us Weekly on the red carpet.

A rep for Jones, 33, told Us last month that the star "is happy to announce that she is expecting her first child this fall."

Michael Fassbender, who plays Erik Lehnsherr/Magneto in the action flick, went into more detail about his co-star.

"She's a fantastic person," the 34-year-old actor told Us. "She's very sweet. Just in the experience of working with her, she sort of gets up and gets on with it, and I think she'll probably do the same in motherhood."

And while her co-stars Byrne, Fassbender, James McAvoy, Kevin Bacon, and Lucas Till were positive for the mom-to-be, they also kept mum on who the father is.

"You know you can't ask me that!" laughed Bacon, who plays Sebastian Shaw.

The Mad Men actress, who plays Emma Frost in X-Men: First Class, is keeping the details of her pregnancy private, including the identify of her unborn baby's father. This will be her first child.

Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!

Want stories like these delivered straight to your phone? Download the Us Weekly iPhone app now!