Former US First Lady Barbara Bush, wife of a former President and mother of another, died on Tuesday at the age of 92.

She had been in failing health for some time, a family spokesperson said.

Her husband George Herbert Walker Bush, a former US president (1989-1993), and her son George Walker Bush, also a former President (2001-2009), were by her side along with other family members when she breathed her last at her Houston home.

“A former First Lady of the United States of America and relentless proponent of family literacy, Barbara Pierce Bush passed away Tuesday, April 17, 2018 at the age of 92,” said a statement from the office of her husband.

Funeral arrangements would be announced as soon as is practical, the statement said.

She is survived by her husband, five children and her brother Scott Pierce, as well as 17 grandchildren and seven great-grandchildren.

The cause of her death has not yet been revealed, but a family spokesman had said on Sunday she decided to refuse further medical treatment, except for “comfort care”, Efe reported.

Barbara Bush had been suffering from chronic obstructive pulmonary disease for some time, which had affected her cardiac capacity and led to hospitalisation on numerous occasions over the past years.

She was last hospitalised for bronchitis in January of 2017 alongside her husband, who was being treated in the ICU.

“Barbara Bush was a fabulous first lady and a woman unlike any other who brought levity, love, and literacy to millions. To us, she was so much more. Mom kept us on our toes and kept us laughing until the end. I’m a lucky man that Barbara Bush was my mother,” George W Bush said in a statement released by the George W. Bush Presidential Center.

Born on June 8, 1925 in New York, Barbara Pierce — her maiden name — was the second woman in the US history to be the wife of one US President and the mother of another, the first being Abigail Adams in the early 19th century.

Bush spent her childhood in Rye, New York, before moving to South Carolina to attend the prestigious Charleston boarding school Ashley Hall, according to the White House.

US President Donald Trump and First Lady Melania said Barbara Bush as a wife, mother, grandmother, military spouse, and former First Lady, was an advocate of the American family.

“Amongst her greatest achievements was recognising the importance of literacy as a fundamental family value that requires nurturing and protection. She will be long remembered for her strong devotion to country and family, both of which she served unfailingly well,” Trump said.

In another statement issued by his campaign, Trump said the former First Lady would always be remembered for bringing strength and dignity to the White House, the Presidency, and America.

“Because of Mrs. Bush’s dynamic personality and devotion to her family, she will serve as an inspiration for future generations of Americans to come,” Trump said.

“Barbara Bush always approached her responsibilities with great integrity, and will also be remembered for her humility and understanding of the challenges of everyday Americans,” he said.

Melania Trump also expressed condolences at Barbara Bush’s demise.

“Throughout her life, she put family and country above all else.Her dedicated service to the American people was matched only by her compassion and love of family,” Melania Trump said.

“She was a woman of strength and we will always remember her for her most important roles of wife, mother, and First Lady of the United States.My heartfelt condolences and prayers are with the Bush family as we honour her legacy,” she said.

Barbara Bush became very popular in her country as an advocate for universal literacy, a cause for which she actively participated with various organisations and to which she felt very close as her son Neil was diagnosed as dyslexic.

The former first lady continued her crusade for literacy and created her own foundation, “The Barbara Bush Foundation for Family Literacy,” which globally supports organisations that promote reading habits among children and adults.

Barbara Bush, the New York native and longtime Texas resident served as America’s first lady beginning 1989 — when her husband was elected as the President of the United States — till 1993.

Later, her son George W. Bush served as the US President from 2001 until 2009. Her son Jeb Bush was the 43rd governor of Florida, and also a 2016 Republican presidential candidate.

Known for her wit and fortitude, Bush spent her final years with her husband in their homes in Houston, Texas, and Kennebunkport, Maine. When asked if she planned to follow her skydiving husband’s lead and take a leap on her milestone 90th birthday in 2015, the former First Lady had told media: “I’m too smart to jump out of a perfectly good plane. I am not jumping out of an airplane. I am not an idiot.”

She also wrote multiple children’s books and published a memoir Barbara Bush: A Memoir and Reflections: Life After the White House in 2003. In 1992, she also authored Millie’s Book, written from the perspective of the first dog.

In a statement, Jeb Bush said he was “exceptionally privileged” to be her son.

Former US President Barack Obama and First Lady Michelle said she was the rock of a family dedicated to public service.

“Barbara Bush was the rock of a family dedicated to public service, and our thoughts and prayers are with both Presidents Bush and the entire Bush family tonight. We’ll always be grateful to Mrs. Bush for the generosity she showed to us throughout our time in the White House, but we’re even more grateful for the way she lived her life – as a testament to the fact that public service is an important and noble calling; as an example of the humility and decency that reflects the very best of the American spirit,” the Obamas said in a joint statement.