Oscar-winning actress Charlize Theron was notified of her very close friend Heath Ledger's passing on Tuesday while walking the carpet at the Sundance Film Festival for her independent thriller "Sleepwalking."

According to an eyewitness, an entertainment media outlet asked Theron how she was feeling about the tragedy, as numerous cameras rolled just moments after the news broke.

Theron, however, had not been informed.

"Charlize put her head down and was ushered into the screening almost straight away," our source said. "She was shaking and her people were really upset about how it all went down."

After this "bad experience," Theron canceled the carpet of the "Sleepwalking" post-premiere party as she did not want to be questioned on the issue.

Meanwhile, fellow Australian and former girlfriend of Heath Ledger Naomi Watts canceled press at the Park City, Utah, festival following the news of the 28-year-old's sudden death.

Watts had been scheduled to hold one-on-one interviews with numerous media organizations on Wednesday morning to promote the highly anticipated "Funny Games."

However, FOXNews.com since has been advised that the press day will not take place due to Watts' emotional state. The couple met on the set of "Ned Kelly" in 2002 and were romantically linked until April 2004.

The publicists stationed in Park City, however, have been working overtime in an attempt to shield stars from the spotlight with various celebrities "calling in sick" to scheduled events.

However, "Alpha Dog" star Lukas Haas spoke to FOX soon after hearing the news, expressing his shock and extending his condolences to the Ledger family.

"He truly was a great, great actor who I have known and admired for sometime," Haas said. "I am in total shock — it certainly has put a damper on the festival."

Later that evening, the stars paid their respects at the Hollywood Life House party in honor of the romantic comedy "The Deal."

"It is so upsetting — it's a huge loss and my heart goes out to his wife and kid," said William H. Macy. "I think great talent comes coupled with great demons."

Young Hollywood sensation Jason Ritter then removed his hat, telling us that "very few actors of Heath's age could leave behind such a legacy of extraordinary work."

"Heath was an actor who always amazed me — somebody I believed always had such life left in him," added "You Raise Me Up" singer Josh Groban.

Fellow Australian A-lister Nicole Kidman also released a statement on Tuesday (via her publicist) saying that "her heart goes out" to his family over such a "terrible tragedy."

The "Brokeback Mountain" sensation no doubt had a huge presence in Hollywood, and his tragic death has rocked the entertainment community.

Lindsay Lohan (who apparently was very close to Ledger) was spotted sobbing as she left a cafe on Tuesday afternoon, while Pop Tarts caught a very shaken Josh Hartnett in shades as he attempted to remain incognito at the film festival soon after the word was out.

Most recently, the 28-year-old "10 Things I Hate About You" star was romantically linked to another Perth-born beauty, 19-year-old supermodel Gemma Ward. The pair was sighted together in Sydney last December — however, Gemma also resides in New York City (where Ledger, too, had a home base).

A close hometown friend of Gemma had not spoken to her since the tragic events unveiled but said she was "deeply concerned" about how the young model would handle the news.

"They have a lot in common — they were both shining stars in their small Perth-based community," said the friend (who did not want to be named). "I can't believe it and I am really worried for Gemma. She will be devastated."

Ledger reportedly gave guidance to Gemma through the filming of her first feature late last year, "The Black Balloon" alongside Toni Collette.

No Show: Sienna Miller 'On a Leash'?

The mere idea that British beauty Sienna Miller would be strutting into Sundance was causing a stir — however, hundreds were left disappointed when she was a sudden no-show at the premiere of "Mysteries of Pittsburgh" on Sunday.

Apparently "work commitments" in London at the last minute prohibited Miss Miller from even making it into the country — however, an insider told Tarts that there were also potential publicity problems.

"Sienna's people have her on a leash," said our source prior to the festival. "Everything she does is being monitored and she won't be doing much media."

Well, it turned out to be none at all ... and nobody really knew why.

"I wish she was here," co-star Mena Suvari said. "Apparently she had a commitment she couldn’t get out of — it is a shame."

Hmmm ... we don't doubt that the A-list actress is in high demand and working hard, but could it also be that someone wanted to keep Sienna a little more silent? Miller made not-so-nice comments about the filming location of Pittsburgh to Rolling Stone magazine (which she was later "advised" to retract).

However, a film insider has told Pop Tarts that it was a "blessing in disguise" that Miller was away from the limelight at this point, as she played Ledger's love interest in the 2005 adventure comedy "Casanova" and the two remained "extremely close."

"He was great — he really took care of me like a big brother," she said while doing press at the time of the film's release. "We both don't take life too seriously and he is just so warm and generous. We had so much fun together."

Ronson and Olsen Party in PJs

Pop Tarts has been told that both celeb DJ Samantha Ronson and actress Mary-Kate Olsen are taking the news of Heath Ledger's death extremely hard, but it was just a few nights ago that the gals were all giggles.

Samantha sang an acoustic set at the Scanty Pajama Party at Sundance's Stereo on Saturday night, and the normally unsmiley Olsen twin snuck in through the back door to avoid the packs of paps awaiting.

The Tinseltown tiny cozied up to "Terminator 3" star Nick Stahl in the corner, both decked out in their neat nightwear, complete with nicotine.

Perhaps MK, Ronson and Stahl were so stimulated after bringing awareness to the Clothes Off Our Backs charity (to assist various children's organizations worldwide) that they decided to heat up with another humanitarian hottie who was waiting up the hill.

"We're going to hang out with Bono," Olsen whispered.

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