In a dramatic example of the collision between her personal and public lives that have marked Robin Roberts' journey over the past year, just after a doctor warned her blood disorder could kill her in just one to two years, she heard she would interview President Obama.

Roberts was at her first appointment with a specialist in myelodysplastic syndrome or MDS. He showed her a graph.

Watch the full story on "A Special Edition of 20/20: Robin Roberts' Journey" Friday at 10 p.m. ET

"There was one year, two years, and a dot in the middle," Roberts said. "And the doctor kept pointing to that dot in the middle, between one year and two years. And I said, What's that? And the doctor said, 'If you don't do anything, that is your life expectancy.'"

When Roberts got in her car and turned on her phone, there were several urgent messages, she said.

"I remember calling [ABC News President] Ben Sherwood from the car, and he's going, 'Where have you been?' And I said, Oh, I had an appointment, sorry, I've been away from the office. What's going on? And he said, 'The White House has called. You're interviewing the president tomorrow at the White House."

Roberts' initial excitement was followed by a more surprising reaction, she said.

"I said, Ben, [I'm] very excited. … It's a privilege and an honor always to interview the president of the United States. Can I get back to you? … I'm just dealing with some - I promise, I'll get right back to you."

"I could only imagine what Ben must have been thinking," Roberts said with a chuckle.

"That's not the reaction that normally happens when you're calling one of your greatest journalists and anchors and telling her the president wants to meet you, and he may have some very big news to break," Sherwood said. "'I'll call you back'? I remember putting the phone down, and I remember thinking, That is so strange. Something's going on."

The interview took place on May 9, 2012, and Roberts still harbored her health secret, she said.

"Again, no one knows all these things that are going on, and, you know, [I] sit down and ask the president, Are you still opposed to same-sex marriage? He makes his historic response … everyone's talking about it, and I'm just going like, People, I have MDS. I have a bone marrow transplant in my future," Roberts said with a laugh.

Watch the full story on "A Special Edition of 20/20: Robin Roberts' Journey" Friday at 10 p.m. ET