(CNN) As he fought the brain cancer that would take his life, John McCain would often sit in his favorite spot on the porch of his Arizona cabin on the Oak Creek, and listen to the famous ancient Irish song "Danny Boy."
One day, when his friend and former campaign manager Rick Davis was there with him, McCain said he wanted "Danny Boy" sung at his funeral.
Davis suggested that award-winning opera singer Renee Fleming be the one to sing it, and McCain teared up.
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Several weeks ago, Davis formally requested that Fleming sing at Saturday's service at the National Cathedral.
"I'm so incredibly touched that he asked for this and that he asked for me to sing it. I'm very moved by that," Fleming told CNN in an interview.
Fleming is starring in "Carousel" on Broadway, and missing a performance is no small thing. She had to get permission from the producer, Scott Rudin.
"It is a big deal, actually, and typically it would be denied for almost anything, because our commitment is to the Broadway theater and to the audience in NY. But Scott Rudin immediately said, 'Yes, of course you must go,' " Fleming said.
To be sure, Fleming has sung at many a big event, from a Nobel Peace Prize ceremony to the Olympics. She even sang "Danny Boy" at the Kennedy Center in 2013.
But she says singing it at a sendoff for McCain, at his behest, is an unparalleled honor.
"He stood so much for the American values that I certainly treasured growing up; for independent thinking, for collaboration and that extraordinary work ethic. He actually came back and said, 'You know what, we're not getting anything done.' I think that resonated with so many people. He also, you know -- because you disagree with somebody, you're not their enemy. There were so many things that he stood for, I think, that we -- many of us -- care about," said Fleming.
She said she met McCain only once, when she sang for him and Barack Obama during the 2008 campaign, at the Al Smith dinner. Appropriately, that is traditionally the one time during a presidential campaign that the two sides come together for a roast and some entertainment.
As for the song, "Danny Boy," Fleming has said it reminds her of her own father.
" 'Danny Boy' is like other great folk songs, something universally loved. And whether it's 'Amazing Grace' or 'Ave Maria,' there are certain songs that affect everyone all over the world in a similar kind of way. Music is the international language. It's the language without words, and we speak it naturally. We don't have to be taught to appreciate music when we're infants, toddlers, etc.," she said.
The lyrics, of course, so poignant:
"Oh Danny boy, oh Danny boy, I love you so
But when you come, and all the flowers are dying
If I am dead, as dead I well may be
You'll come and find the place where I am lying
And kneel and say an 'Ave' there for me."
"It's so beautiful," remarked Fleming, "and 'my dreams will warm and sweeter be.' It's an incredibly beautiful lyric. And there's a lot of people who say it's their favorite song and it never fails to make them weep."