Kelly Osbourne may be back to her partying ways. Which could be one possible explanation for those horrible corpse photos from the weekend. According to Radar, Kelly has “fallen off the wagon” in a big way, having been sober since 2009, when she was in rehab for her drug and alcohol addictions. Here’s the thing, though – I have doubts as to whether Kelly was ever really committed to being “on the alleged wagon.” I’ve heard stories about her drinking and drugging post-rehab. I’m just sayin’. Here’s Radar’s report:

After nearly three years of sobriety, Kelly Osbourne has fallen off the wagon and is back to boozing, RadarOnline.com has exclusively learned.

The 27-year-old daughter of Sharon and Ozzy Osbourne got clean in February of 2009 after completing a rehab stint for drug and alcohol addiction, but according to several sources the fashionista is back on the bottle.

“Kelly is definitely off the wagon again — at least when it comes to drinking,” an insider tells RadarOnline.com. “I’ve seen her out drinking cocktails, beer and champagne numerous times, and I’ve seen her pretty unsteady on her feet too.”

And just this past Sunday, Kelly guzzled cocktails at the Golden Globes after-party and got so wasted (as evidenced by the exclusive photo) that she almost fell over.

“Kelly was so wasted,” an eyewitness who partied with the Fashion Police host tells RadarOnline.com. “At one point she almost fell back and I had to catch her!”

According to the party pal, once Kelly gets alcohol in her system the claws come out in full force and she doesn’t hold back about her constant feuding with Christina Aguilera.

“When she gets drinking her hatred for Christina Aguilera really comes out,” the source said. “She spent the entire night talking about how much she hates Christina!”

The outspoken Brit and Christina have been battling for years, most recently with the newly slimmed-down Kelly poking fun at the Dirty singer’s curvy new figure.

“She called me fat for years. I was never that fat,” Kelly said on E! Fashion Police about Christina’s appearance at the Michael Jackson tribute concert.

And in September Kelly ranted about Christina’s bullying saying, “She called me fat for so many f***ing years. So you know what? F**k you! You’re fat too.”

“This is the side of Kelly that comes out when she’s drinking,” one of the sources told RadarOnline.com.

“Maybe she thinks it’s OK for her to be drinking as her past problems were pills, but as far as I know if you want to be ‘sober’ you need to be SOBER, period.”

Attempts to reach Kelly’s rep for comment were unsuccessful at time of publication.

[From Radar]

Sure. I’ll buy that. All of it, actually. I think she’s probably still drinking, and I’ll buy that she bitches about Christina Aguilera when she’s wasted. The problem isn’t that Christina bullied Kelly (which probably did happen) – the problem is that both Christina and Kelly are boozehound monsters.

Also – did you realize that Kelly is 27 years old? For whatever reason, I thought she was younger than that. I tend to think that when “celebrities” struggle with alcohol and drug problems very early, and then go into rehab and start with the program at a young age, that they’re more likely to relapse later. Not to get all psychoanalytical, but I imagine it’s difficult to be only 22 or 23 years old and think, “Hey, I’m 22 and I can’t have a drink for the rest of my life.” I’m not saying that as a justification, merely as an explanation for why Kelly seems to be back to her partying ways.

(PS… Do you know why I stopped drinking to excess – and why I’ve only been drunk-ish once in a year? I don’t want the extra calories. Instead of making it about sobriety, I’ve made it about empty alcohol calories, and it works for me. I bet it would work for Kelly too.)

Photos courtesy of Fame, WENN.