Star magazine reports Jessica's hot on her sister's matrimonial heels, and may just beat her down the aisle.

"(Jessica would) love nothing more than to get married before Ashlee," a source revealed to Star. "It upsets her that her little sister will be married and she won't. She gets jealous when Ash gets more attention."

That's where Jessica's six-month romance with Dallas Cowboys quarterback Tony Romo comes in. "She's been showing him rings in magazines," the insider said. "She tells him what she likes, and she does it right in front of his friends, too, so it's really awkward."