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Here's Brit just a half hour ago as she braved the paps to do some shopping at Lisa Kline in Beverly Hills. She told our cameraman her sister's NOT PREGNANT!

But is Brit just unaware of the news? Did Jamie Lynn forget to mention it to her sister? Are Jamie Lynn and her mom Lynne not talking to Britney -- again? What's going on here?!

Video coming soon -- stay tuned! ...