Rachel Uchitel - best known as Tiger Woods' mistress #1 - is checking into Celebrity Rehab, RadarOnline.com has learned.

Uchitel, 35, will appear on the fourth season of VH1's Celebrity Rehab with Dr. Drew. Uchitel, a New York party planner, will be treated for an addiction to pills, according to the New York Post who cited a network source.

The paper says the source did not specify what kind of pills Uchitel has an addiction to, although, as RadarOnline.com has previously reported, Uchitel was known to have taken the sleeping pill Ambien with Tiger while they had sex.

At first glance, it seemed like an unlikely pairing --  millionaire Brit heiress Petra Ecclestone and Hollywood's convicted felon heir Brandon Davis sharing a friendly lunch Saturday -- but RadarOnline.com has photos.

Actually newlywed Petra, heir to daddy Bernie Ecclestone's Formula 1 fortune and Davis, whose granddad was oil mogul Marvin Davis, have been acquaintances for years and have mutual friend Paris Hilton in common.

PHOTOS: Petra Ecclestone Hangs With Brandon Davis In NY

Casually dressed in a plaid shirt, Davis joined Ecclestone and her husband James Stint, for a laid back lunch at Nello restaurant.

Davis reportedly was the one who suggested to 22-year-old Ecclestone that she purchase Candy Spelling's 57,000-square foot, $85 million mansion, a deal which Paris' dad, Rick Hilton, a real estate broker, handled.

PHOTOS: Petra Ecclestone Weds

Paris and the rest of the Hilton family were among the 250 lucky guests to attend Petra's $6.5 million wedding to Stint at in a castle in the Italian town of Bracciano last month.

While Petra has recently made headlines because of her massive fortune and big spending habits, her L.A. pal most often catches the attention of the media -- and the police -- due to his hard-partying ways.

PHOTOS: Meet The Ecclestones - Petra And Her Family

As RadarOnline.com previously reported, Davis, 32, was arrested in April for felony drug possession and assault following an incident at the Roosevelt Hotel in Hollywood.  In June, he pleaded guilty to the cocaine possession charge and no contest to battery, a misdemeanor, for which the judge sentenced him to a drug diversion program.

Back in 2006, Brandon checked into the famous Promises rehab facility at a cost of $75,000-per-month.

PHOTOS:  Petra And Tamara Ecclestone Double Date In Hollywood

Brandon’s brother Jason has had several drug-related arrests of his own, including one just days after he completed shooting the latest season of Celebrity Rehab.

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UPDATE: Brandon Davis was released from jail at 11:13 am PDT after posting $10,000 bail.

PHOTOS: Brandon Davis Released From Police Station

Hollywood heir Brandon Davis was arrested at 4:25 am Thursday, and RadarOnline.com has the “Inmate Information” sheet showing he still hadn’t bailed out more than five hours later.

Read The Sheriff’s Department Document Here

Davis was put into handcuffs following an incident involving battery and possession of a controlled substance.

When an overdose landed Jason Davis into Cedars-Sinai Medical Center last January, his father literally begged him to go from the hospital straight into in-patient rehab, RadarOnline.com can exclusively reveal.

Now, as RadarOnline.com reported Friday, Davis has been busted again for possession of a controlled substance.  It happened just a day after the live reunion episode of Dr. Drew's Celebrity Rehab, which had featured Davis in the cast.

PHOTOS: Lindsay Lohan Happy Out Of Rehab

Davis' father, Nebil Zarif made several trips to Cedars last January to see his son, a well-placed source tells RadarOnline.com exclusively.  "He was literally begging Jason to go directly into rehab once he was medically stablized. He was so concerned, he even brought in an addiction specialist who also tried to convince Jason.

"The two men discussed Jason needing a minimum of 90 days in-patient to get clean."

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Jason refused, and would only promise to attend out-patient counseling, the source says.  He subsequently joined Dr. Drew's cast of misfits for Celebrity Rehab, and it wasn't long before he was back using.

Davis, the son of wealthy socialite Nancy Davis -- he and his brother Brandon both took their mother's last name several years ago -- is currently free on $20,000 bail.

PHOTOS: Celebs In Rehab

"My son is an addict," Nancy Davis told RadarOnline.com last year.

Maybe now that Martin Sheen has convinced his son Charlie to go back into rehab, he can share some advice with Jason's dad.

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Celebrity Rehab graduate Jason Davis was arrested Thursday night for possession of a controlled substance, RadarOnline.com has confirmed.

The grandson of late billionaire business mogul Marvin Davis was arrested in Newport Beach, California, just one day after the live reunion show aired for Celebrity Rehab in which Dr. Drew drilled him about his sobriety.

Davis admitted to relapsing twice, but claimed he's been sober for 90 days.

PHOTOS: Lindsay Lohan Happy Out Of Rehab

"I went off to Newport and, well, let's just say I started a new life, but I finally got it this time," Davis said.

He's currently being held on $20,000 bail and is no stranger to trouble with the law.

PHOTOS: Life's A Beach For Tiger Woods' Mistress Rachel Uchitel

Davis was hospitalized last January for his drug problem and has admittedly struggled with an addiction to heroin.

He created headlines and controversy when Tom Arnold tried to help him and instead got caught in a vicious backlash of accusations.

Davis' mother Nancy Davis told RadarOnline.com at the time about Jason: "My son is an addict."

PHOTOS: Celebs In Rehab

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It looks like actor Jeremy London, 70s heartthrob Leif Garrett and paunchy socialite Jason Davis did more than just conquer their demons in Celebrity Rehab 4: They made new friends, as well.

PHOTOS: Celebrity Rehab 4's Three Amigos Bond In Hollywood

The troubled trio were seen hanging out on the Hollywood Walk of Fame Thursday, and RadarOnline.com has all the pictures for you.