It looks like newly engaged lovebirds Ashlee Simpson and Pete Wentz have more than just their upcoming wedding to celebrate. OK! can exclusively reveal that the pop star is also pregnant with the couple’s first child! The baby is due in October, and the parents-to-be are ecstatic with joy.

Ashlee, 23 and Pete, 28, have been together just 18 months but are as “perfect for each other as any two people could be,” a friend of the couple tells OK!. “They don’t spend a minute apart if they can possibly avoid it and are over the moon about the baby.”

Unfortunately none of that happiness was enough for Jessica Simpson‘s little sis to overcome a fierce bout of what appeared to be morning sickness when OK! caught up with her at the Chart House restaurant in Malibu on April 12.

The singer and and her Fall Out Boy beau were there along with her family to celebrate the college graduation of his assistant. But the moment they arrived at the oceanfront restaurant, Ashlee made a mad dash for the ladies room, leaving her fiancé waiting anxiously at the door!

The under-the-weather Ash, drinking only water, looked thoroughly ill but still did her best to enjoy the luncheon. Pete, however, was in great spirits, though his thoughts were clearly never far from Ashlee. "He was holding her hand the whole time," a witness tells OK!.

Meanwhile, the first-time mom and dad are busy putting together a wedding. “They’re planning on something in the Santa Barbara area probably by the end of May,” the friend reveals to OK!. “Ashlee would like to walk down the aisle before she’s showing — although she’s very cute the way she’s always checking out her belly now and asking everyone, ‘am I showing yet?’"

The source also tells OK! that the singer is leaning toward Vera Wang for her gown while Pete and his groomsmen are likely to be dressed in Dolce & Gabbana.

"Pete may personally design their wedding bands,” the friend says. “He designed the diamond and silver ‘promise ring’ he gave Ashlee last October.”

As far as Ashlee’s choice for her maid-of-honor — that’s an easy one. Big sister Jessica already has the nod and Ashlee may be soon returning the favor. “I don’t think Jessica and Tony [Romo] are that far behind!”

Ashlee is already planning on juggling motherhood and career. Her next album, Bittersweet World, drops on April 22. Her line of shirts for Wet Seal hits stores the same day. Fall Out Boy also just released a new CD, Live in Phoenix.

For the whole story, pick up the next issue of OK! — on newsstands everywhere Thursday!

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