It's official: Reese Witherspoon and her husband of four years, actor Ryan Phillippe, will become parents for a second time, the "Legally Blonde" star confirmed to Jay Leno on the "Tonight" show.

After much speculation (but no official confirmation from the mom-to-be), Witherspoon, 27, said she and Phillippe, 28, learned they had a new baby on the way after returning from a second honeymoon in the Caribbean. The arrival is reportedly due in December.

The announcement also apparently delighted the couple's daughter, Ava Elizabeth Phillippe, who turns 4 in September. "My daughter is so excited," Witherspoon told Leno.

"She's making lots of preparations around the house. The other day she told me: 'Mommy, the baby needs something -- cheese snacks.' We had to go to the store and get lots of cheese snacks."

Last month, it was announced that Witherspoon, who stars in the upcoming sequel "Legally Blonde 2: Red, White & Blonde" (for which she was reportedly paid $15 million) would play June Carter, wife of country legend Johnny Cash, in the film bio "Walk the Line."

Joaquin Phoenix is reportedly playing the man in black, though there has been no start date announced.

Now, it is being reported, next month Witherspoon will begin shooting an adaptation of William Makepeace Thackeray's classic 1840s novel "Vanity Fair," which was the role model for author Margaret Mitchell when she wrote "Gone With the Wind."

Like Scarlett O'Hara, the spirited -- some would say ruthless -- heroine of "Vanity Fair," named Becky Sharp, lets nothing stand in the way of her improving her social standing.

James Purefoy ("A Knight's Tale") has been announced as costar.