Outside, in the street, a crowd of fans had already gathered with placards, banners and even an ebullient fellow from Dallas waving what he called the world's largest wristband, hailing his heroine. It read, "Welcome Back Robin."
Once the show hit the air, Roberts, with her colleagues surrounding her, looked into the camera, broke into a great big smile, and announced: "Hi, it's Robin. I've been waiting 174 days to do this: Good Morning America!"
Said her co-anchor George Stephanopoulos: "We've been waiting for that drumroll. It is official now. Welcome back, Robin."
From Jimmy Kimmel and Bradley Cooper, sitting at Kimmel's talk show desk in Hollywood: "Welcome back, girlfriend." Also chiming in as the show played on: Oprah Winfrey, and then Hillary Clinton, who said good-naturedly she had no job prospects at the moment so would be free to watch Roberts.
The rival Today show sent a gift basket and made a significant donation to the charity that facilitates finding bone-marrow matches.
And from 1600 Pennsylvania Avenue: "Good morning, America, and welcome back, Robin," said President Barack Obama, First Lady Michelle Obama sitting with him.
"Robin," said Mrs. Obama, "we just want you to know that the whole Obama family, we've been thinking about you, and praying for you, and rooting for you every step of the way."
"You've been an inspiration to all of us," said the President, "and we couldn't be happier that you're back here, doing what you do best."
Said Roberts, 52 – besides claiming she wasn't wearing the froggy slippers she had sported around her apartment ("Or, am I?" she said) – "I keep pinching myself and I realize that this is real. This is really happening.
"Faith, family and friends have brought me to this moment and I am so full of gratitude."
Her medical team was introduced later in the show. Before that, Roberts said, "There's so many people that I want to thank throughout the morning, my doctors and nurses and family and colleagues and people who have sat in this chair and those who have blazed the trail before me."
"As my mother said, 'We all have something.' Everyone’s story has purpose and meaning and value, and I share this morning, this day of celebration with everyone."
She added later, after witnessing an impromptu jam session taking place in her honor outside the studio, "Our viewers have been incredible."
Roberts recently received the all-clear from her doctors, as tests have shown no abnormalities and she has continued to gain strength. She had already been back in the studio, doing a series of dry runs before her official return Wednesday.
A special edition of 20/20 on Feb. 22 will offer a behind-the-scenes look at Roberts's experience and those who have been inspired by her example.