Michelle Obama has written about how much she struggled to deal with the Sandy Hook massacre in her new memoir.
In her book, which is released today, the former first lady says she was affected by it so much that she couldn't go with her husband to the vigil, according to exclusive excerpts seen by NBC's Today Show.
She also says on the day of the shooting, Barack Obama, for the first and only time in his eight years as president, requested her presence in the Oval Office, where they embraced and had "no words".
"This would be the only time in eight years that he'd request my presence in the middle of a workday, the two of us rearranging our schedules to be alone together for a moment of dim comfort.
"Usually, work was work and home was home, but for us, as for many people, the tragedy in Newtown shattered every window and blew down every fence," she wrote.
"When I walked into the Oval Office, Barack and I embraced silently. There was nothing to say. No words."
Adam Lanza, 20, killed 20 children, six adults and himself within 11 minutes at Sandy Hook Elementary School in Newtown, Connecticut on 14 December 2012.
The children were aged six and seven.
Mr Obama wiped away tears as he addressed the nation following the incident.
"Staying upright after Newtown was probably the hardest thing he'd ever had to do.
"When Malia and Sasha came home from school later that day, Barack and I met them in the residence and hugged them tight, trying to mask the urgency of our need just to touch them," Mrs Obama recalled.
"It was hard to know what to say or not say to our girls about the shooting. Parents all around the country, we knew, were grappling with the same thing."
In her memoir, Mrs Obama says she would regularly provide comfort to people affected by tragedy, including bereaved relatives of military members, victims of natural disasters as well as victims of mass shooting, but she says Sandy Hook was too much for her to bear.
She explained why she couldn't go with her husband to a prayer vigil two days after the tragedy.
"I was so shaken by it that I had no strength available to lend. I'd been First Lady for almost four years, and there had been too much killing already – too many senseless, preventable deaths and too little action.
"I wasn't sure what comfort I could ever give to someone whose six-year-old had been gunned down at school."
The former first lady's book describes her upbringing on Chicago's South Side, as well as her time at Whitney Young and Princeton University.
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She visited her old Chicago high school ahead of its release to discuss the memoir with current students.
In excerpts the students received, Mrs Obama writes about straddling economic and social worlds as a child and young adult. She writes that she knows her anxiety was part of a "universal challenge of squaring who you are with where you come from and where you want to go."