Jennifer Aniston to be the "surprise" guest on season finale of Oprah's Big Give

Jennifer Aniston will be the "surprise" guest on the season finale of Oprah's Big Give this Sunday, Winfrey's pal Nate Berkus has confirmed.

"I have known Jen for years and she is an awesome woman," Berkus told the New York Daily News at the launch of Belvedere vodka's Jagger Dagger.

"Jen's wonderful and generous," he said. "She is a huge part of Sunday night's show and people will be surprised to see how big a part she plays in the actual Big Give."

The Big Give, which focuses on 10 contestants as they travel across the country with a large sum of money, and try and help people in unique ways, has already inspired many celebrity donations, including one from American Idol judge Simon Cowell, who gave $162,000 to a couple whose 3-year-old daughter Madeline was diagnosed with a rare and aggressive form of cancer.