U.S. President Barack Obama has ordered flags at the White House and all federal buildings to be lowered to half-staff "as a mark to respect the memory of" former first lady Nancy Reagan.
The steadfast partner of the 40th U.S. president, Ronald Reagan, Nancy Reagan died Sunday of congestive heart failure at the age of 94.
She will be buried beside her husband at the Ronald Reagan Presidential Library in Simi Valley, California, on Friday.
A White House statement issued Monday said Obama called for flags to remain at half-staff at federal government buildings, military posts, U.S. naval vessels and diplomatic missions until sunset on the day she is buried.
Obama said he and first lady Michelle Obama met Nancy Reagan once, after he took office in 2009, and that she could not have been more charming and gracious to the new White House occupants.
He said the former president "was lucky to have her, and I'm sure he would be the first to acknowledge that, so she will be missed."
On Sunday, the Obamas said in a joint statement that Nancy Reagan “redefined the role” of first lady during her tenure.
“Nancy Reagan once wrote that nothing could prepare you for living in the White House. She was right, of course. But we had a head start, because we were fortunate to benefit from her proud example, and her warm and generous advice,” their statement said. “We remain grateful for Nancy Reagan’s life, thankful for her guidance, and prayerful that she and her beloved husband are together again.”
WATCH: President Obama Talks About the Passing of Nancy Reagan
Many other touching tributes have been pouring in for the former first lady, renowned for her devotion to her husband, whom she called "Ronnie."
Former first lady Barbara Bush said in a statement, “Nancy Reagan was totally devoted to President Reagan, and we take comfort that they will be reunited once more.”
Life with Ronald Reagan
Born Anne Frances Robbins, she was given the name Nancy by her mother. Having caught the acting bug from her mother, young Nancy pursued the profession in New York and Hollywood, where she met fellow actor Ronald Reagan.
The couple married in 1952.
The former Nancy Davis made 11 films in all, her last one coming in 1956: Hellcats of the Navy, co-starring her husband.
Ronald Reagan was governor of California from 1967 to 1975. Following a failed presidential bid in 1976, he subsequently won back-to-back elections in the 1980's.
In Photos: Nancy Reagan
'Just Say No' campaign
As first lady, Nancy Reagan spearheaded the "Just Say No" campaign against substance abuse, carving a space for herself in the national movement to combat recreational drugs.
A regular presence by her husband's side, Nancy Reagan also was sharply criticized for extravagant spending at the White House at a time of high unemployment in the United States.
By all accounts, the couple remained close until the former president died in 2004 after a decade of living with Alzheimer's disease.
They are survived by two children, Patti Davis and Ron Reagan.