While Rob Pattinson was busy smoking up a storm on his balcony, Ashley Greene and fellow Twilight cast members Peter Facinelli and Jackson Rathbone were spotted leaving the Century City Plaza Hotel over the weekend after the "Welcome to The Twilight Saga" panel. Ashley kept it casual in a simple pantsuit and neutral suede pumps, and it's clear that all those hours at the gym have paid off -- girlfriend looks AMAZING!

Last week Rob, Kristen Stewart and Taylor Lautner had their hands immortalized in cement on Hollywood Blvd, so it looks like the Breaking Dawn frenzy is in full force!

Pete Wentz and his model girlfriend Meagan Camper grabbed a meal with his son, Bronx Mowgli, on Sunday.

Wentz was winding down after a crazy weekend -- he performed with his new band, The Black Cards, in Hollywood on Friday, where he told the Los Angeles Times:

"I feel every parent lives a double life. It's the same on some levels — toddler vomit vs. adult vomit. Kidding ... I plan my schedule around my son; he's been all over the world already, from Tokyo to Paris. I try to not ever go too many days without seeing him. On stage, I play music and at home I make fart noises."

Aw! Bronx is, of course, Pete's son with ex Ashlee Simpson. See what he said about Simpson after the jump ...

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Seven years have passed since Mariah Carey released her hit Christmas song "All I Want For Christmas Is You," and now Justin Bieber has joined Mimi for a new re-make. Check out these photos of the twosome on set of the new video. Thanks for sharing the pics, Mariah!

Ms. Carey looks oh-so-cozy on Santa's sleigh. Perhaps the mama of two will be giving Biebs a ride!

The new track is featured on the 17-year-old singing sensation's Xmas album, Under the Mistletoe.

Kelly Osbourne is Tweeting about an injury she suffered in Miami over the weekend.

The 27-year-old was partying at Liv nightclub in Miami on Saturday, but apparently things went awry!

She Tweeted on Sunday:

"I just want 2 thank all the incredible doctors and nurses @ Mercy hospital in Miami 4 taking such good care of me u guys really are amazing! ... Long story short I cracked my head open then kept passing out I have the all clear my mum came 2 get me ... "

She was in the Miami heat to cast models for her Material Girl clothing line with Madonna's daughter, Lourdes Leon.

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When not performing on stage in provocative outfits, Rihanna loves to chill in comfort.

The 23-year-old songstress, rockin' a striped onesie, was hard at work while recording new tracks for her upcoming album Talk That Talk.

RiRi Tweeted, "DONE B***HES!!!!"

Some of the new songs include "Where Have You Been," "Fool in Love" and "Do Ya Thing."

We're loving RiRi's low-key look with barely any eye makeup. However, she still loves that red lipstick ... and we do, too!

See all of Rihanna's casual photos in our gallery below.

Justin Bieber will take a paternity test to prove that he is not the father of Mariah Yeater's baby, People confirms.

Bieber, 17, has been adamant over the past week that 20-year-old Yeater's claims (she says Bieber impregnated her after a Los Angeles concert last year) are completely false.

The teen star says he has never met Yeater, but she is demanding a DNA test in court documents. She is seeking financial support.

A rep for Bieber told the mag:

"It's sad that someone would fabricate malicious, defamatory, and demonstrably false claims. We'll vigorously pursue all available legal remedies to protect Justin and to hold those involved with bringing this suit accountable for their actions."

The "Baby" singer performed at the MTV Europe Music Awards in Belfast, Northern Ireland, on Sunday (which his girlfriend, Selena Gomez, hosted.) He won two awards, including Best Male Act, and will reportedly take the test upon his return to the U.S.

Our X17online poll revealed that 67 percent of readers think that Yeater is lying, while 32 percent of you believe Bieber IS the father of her baby.

Katie Holmes put away her usual mom jeans and flats for a flowy black skirt and plunging pink blouse at the premiere for her latest flick Jack and Jill.

Tom Cruise's wifey also gave us a look at her sexy back! We have to admit, Katie cleans up well!

Ms. Holmes' loose skirt makes us wonder if she's hiding a tiny baby bump in there. Now that Suri is already five, the timing seems perfect for baby #2. Not such an impossible mission.

Demi Lovato is all about life changes lately!

The 19-year-old singer changed her hair color over the weekend -- to red! She Tweeted the pic above on Sunday, saying, "Red hurr she don't curr..."

Lovato recently gave an interview to Latina magazine and about her stint in rehab (although we have to ask -- what is left to say?) She told the mag she was afraid she wouldn't have a career after spending time in a facility, and that rehab wasn't totally her idea.

"It was influenced by management, publicists and family," she said. But one person who didn't help was her estranged father. "Sometimes there are people in your life that you have to cut out," she says. "It sucks when it’s your own father."

And did Demi hint at rekindling her relationship with her much older ex Wilmer Valderrama, 31? The two were spotted smooching last week.

"I have an old soul, because I had to grow up fast – because of the public eye and because of my life experiences," she said.

See more from the interview after the jump!