Hello, Leggy Olson!

Elisabeth Moss, who plays dowdy ad exec Peggy Olson on the hit show “Mad Men,” reveals a sexy new persona on the cover of tomorrow’s Page Six Magazine.

“Sometimes, you just want to be a bad girl,” she tells the magazine, free with The Post.

In a Burberry trenchcoat and not much else, Moss hints about “Mad Men’s” fifth season, premiering March 25 on AMC.

“[It’s] very meaningful what happens to Peggy,” she says.

“I am ecstatic. The audience is going to be surprised.”

The March issue of Page Six Magazine also features:

* Super Bowl champ Victor Cruz in his first-ever fashion shoot.

* Chelsea Tyler, lookalike daughter of Aerosmith frontman Steven, now a model and singer in her own right.

* Five fresh fashion trends seen on the street.