An ever glowing, and showing, Jennifer Garner hit "The Tonight Show" Tuesday night, and when Jay Leno asked if she was expecting a boy or a girl, the actress skirted the question, saying, "We have one or the other for sure."

But just minutes later, Garner slipped, letting her and husband Ben Affleck's secret out. "Then I felt just bigger and bigger, like she --," Garner said before gasping and then laughing.

Yes, it seems to be a girl for the happy couple.

Meanwhile, expect more secrets to unfold when "Alias" returns this week. Get set for spies, lies and one big surprise! Only "Extra" has your first look at the series' gripping fifth season premiere, an opener that has Garner (and her stunt double) on the run, with tummy in tow.

"My stunt double is so cute," Garner told us. "She's wearing her little pillow right in front and doing all this stuff."

Garner, who is due in December, also revealed that writers initially wanted to hide her pregnancy. "I was working on a movie this summer and said, ‘I don't think I'm going to have the kind of pregnancy I can hide,'" Garner recalled. "'I'm going to carry it like -- boom -- all the way out. So you might want to rethink it.'"

So the producers did, and they came up with TV daddy Michael Vartan, who is also Garner's ex.

And while we can confirm that Agent Vaughn survives the shocking car crash, rumors are still swirling that Vartan plans on leaving the show.

But Garner assured us, "The answer is no."

See all the action when "Alias" premieres Thursday night on ABC.