Michelle Obama shares what the 'darkest day' was like in the White House: the Sandy Hook elementary school shooting

Jacquelyn Martin/AP

President Barack Obama and first lady Michelle light 26 candles in honor of the Newtown shooting victims, on the one year anniversary of the massacre.

• In her new memoir, "Becoming," Michelle Obama details what the atmosphere was like at the White House after the Sandy Hook shooting in 2012.
• She writes that her husband had her come back to the White House immediately after the shooting, because he needed her comfort.
• Michelle says she couldn't bring herself to attend a prayer vigil for the victims because she was "so shaken" by what happened.

Michelle Obama says there was only one time that her husband called her to his office in the middle of the workday because he needed her support, and that was after the Sandy Hook massacre in 2012.

In her new memoir, "Becoming," the former first lady says she was giving a speech across the street from the White House when news broke that a gunman had shot and killed 20 first-graders and six educators at Sandy Hook Elementary in Newtown, Connecticut, before taking his own life.

When Michelle wrapped up her speech, her chief of staff came up to her and informed her what happened and said that the president wanted her to return to the White House "right away."

White House/Pete Souza

The moment President Barack Obama learned of the shooting.

"My husband needed me," Michelle writes. "This would be the only time in eight years that he'd request my presence in the middle of the workday, the two of us rearranging our schedules to be alone together for a moment of dim comfort."

She continues: "When I walked into the Oval Office, Barack and I embraced silently. There was nothing to say. No words."

As a "fact guy," she says her husband demanded to be fully briefed when it came to events like this. So he was overwhelmed with details of "the graphic, horrid crime scene," of the "blood pooled on the floors of the classrooms and the bodies of" the victims.

This especially disturbed her husband, who "loved children in a deep and genuine way."

YouTube/The Obama White House

President Obama wiped away tears as he addressed the nation following the shooting.

Read more: 25 things we learned from Michelle Obama's new memoir, 'Becoming'

"Staying upright after Newtown was probably the hardest thing he'd ever had to do," she said.

She says when their daughters got home from school that night, they met them in the residence to give them a hug.

Later, she watched as her husband addressed the nation, unable to hold back his tears.

Michelle writes that she was "so shaken" by what happened that she couldn't bring herself to go with her husband to a prayer vigil for the victims.

"I had no strength left to lend," she said.