Billionaire Bails Out Kim Kardashian, Lady Gaga From Twitter Exile

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Pharmaceutical entrepreneur Stewart Rahr pitched in $500,000 toward a $1 million goal for an AIDS charity.

Kim Kardashian and Lady Gaga are back on Twitter, thanks to a billionaire who donated $500,000 to their campaign to raise $1 million for AIDS.

Those stars -- and others like Ryan Seacrest, Alicia Keys, Usher and Justin Timberlake -- vowed to quit Twitter until raising the funds for Keys' Keep a Child Alive. RELATED: Twitter worth $4 billion.

But after about a week (the campaign launched on Dec. 1, World AIDS Day), they still hadn't reached their goal. So on Monday, pharmaceutical entrepreneur Stewart Rahr pitched in $500,000.

"I'm back from the dead! Thank you all so much for your donations and contributions! I have missed u all so much!!!," Kardashian, who can earn $10,000 per sponsored Tweet, posted on Twitter.

Added Seacrest, "So stoked to be back on twitter! Special shout out to Stewie Rah Rah for his generous donation.”

The charity said 3,600 people had given up Twitter for the cause.

"Although we never expected to raise $1 million overnight, we are completely blown away that we were able to achieve our goal in less than a week," the organization said in a statement.