Johannesburg (CNN) -- Daytime TV doyenne Oprah Winfrey said Friday she is "100%" behind President Obama as he campaigns for re-election this year -- and that the man she backed four years ago for president is doing a great job.
Winfrey made the comments in a wide-ranging interview with CNN in South Africa, where she is marking the graduation of the first students to join the academy she set up five years ago.
Seventy-two students, known as "the pioneers," will graduate Saturday from the Oprah Winfrey Leadership Academy for Girls, watched by the school's founder.
The talk-show host opened the school in January 2007 to provide educational opportunities for impoverished girls in South Africa.
In a post on her Facebook page Thursday, Winfrey said: "I am one proud Mama."
The graduation ceremony will be a first for the school, she said, before the students "go their separate ways to colleges all over South Africa and the U.S. A bittersweet day to bask in all the memories of the past five years."
The school has faced a number of challenges over the years, including complaints of abuse against a dormitory matron -- who was later cleared -- and a police investigation into a student last year after an infant's body was found.
But Winfrey emphasized the achievements of the school's 400 pupils, saying the word "disadvantaged" had been eliminated so that no-one would lower their expectations for the girls.
This time four years ago, Winfrey was also helping raise expectations for Obama as he battled for the 2008 Democratic nomination, appearing alongside him at campaign events in Iowa, New Hampshire and South Carolina.
Asked about her support for Obama this time around, Winfrey said she had not felt the need to formally endorse him for 2012 because he is now well known to everyone.
"I don't need to endorse him because I am a 100% supporter of him and I've already endorsed him," she said.
"If he or his office called me tomorrow and said that they needed me I would do whatever I thought would be of service. I did what I did in 2008 because I really thought that would be of value and of service. I don't think that's needed in 2012. There's not a person in the world who doesn't know who Barack Obama is."
Winfrey urges people not to forget how dire the economic outlook was when Obama first took the reins when they assess how well he is doing in the White House.
She says she is confident Obama will be re-elected, adding, "I think he is a masterful leader."
And his biggest challenge if he does indeed win a second term?
"The same thing as the first four years, and that's getting jobs for people, and getting our economy back in order, and building a sense of confidence in the American people so that they know that their futures can be sustainable."
CNN's Robyn Curnow contributed to this report.