Paris Hilton and Doug Reinhardt: Back On!

Less than two months after splitting, Paris Hilton and Doug Reinhardt are back together, Usmagazine.com has confirmed.

"They are definitely happy again," a source close to the couple -- who called it quits in June after four months of dating -- tells Us.

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A rep for Reinhardt has no comment.

On Monday, Reinhardt, 23, posted on Twitter: "What an amazing weekend with my beautiful girlfriend. I love her so much!"

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The day before that, he wrote: "Laying in bed watching SportsCenter with my girl."

Hilton, 28, declared she'd wed Reinhardt -- who dated Lauren Conrad on The Hills -- last April.

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"He's going to be my husband," she told E! "We're best friends. It's not like we just met. We've known each other over the past year. I was in a relationship before and we reconnected. I'm really in love and really happy."