Britney Spears told X17 XCLUSIVELY that her sister is NOT pregnant, saying "My sister is not pregnant!"

We caught up with Brit just minutes ago as she was shopping at Lisa Kline in Beverly Hills and that's what she told us!!!

There is a video @ the Source and guess who else was at Lisa Kline, tailing Britney! ...

KFed's attorney Mark Vincent Kaplan's process server Aaron Cohen was outside the store as Brit shopped inside. Why???

PS: They were like "Yes she is" and she was like "whatever" then she sat in the car looking weird for a few minutes.

But then, Spears friend and E! entertainment reporter Jason Kennedy says that Britney's camp gave him the following exclusive statement:

"Britney is aware of the news regarding Jamie Lynn's pregnancy. She wishes her sister nothing but the best and asks for privacy during this time." - Source

They also say that Britney herself called OK! trying to get an advanced copy of the mag. - Source

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UPDATE: Britney Spears had an unlikely ally outside of the Lisa Kline boutique last night -- with security provided by the same man who just a few months ago had personally served subpoenas on her entire entourage -- on behalf of K-Fed! It's a small security world after all!

Aaron Cohen, a former member of the Israeli Mossad, tells TMZ, "We provide exclusive VIP security for the Lisa Kline... IMS Security knows the level of security required for Britney Spears and know that we are highly capable of providing the standard. We don't discriminate when it comes to physical safety/security."

We spoke to Kate Diamond from Lisa Kline, who told us, "We love Britney ... she's always fun, and she's looking great these days!"

Brit was whisked in and out of the store by Cohen himself -- the only mishap caused by Britney -- who smashed her car door into a car parked next to her! Dang dings!

Source