John McCain's 106-year-old mother is expected to attend his memorial and burial services in Washington and Maryland later this week.

Roberta McCain called her middle son "Johnny." The Vietnam prisoner of war, Republican congressman, senator and two-time presidential candidate died of brain cancer Saturday at age 81.

In one of his books, McCain wrote that his mother "was raised to be a strong, determined woman who thoroughly enjoyed life, and always tried to make the most of her opportunities.

" ... my mother was raised to be a strong, determined woman who thoroughly enjoyed life, and always tried to make the most of her opportunities." — John McCain, referring to his mother, Roberta McCain

"She was encouraged to accept, graciously and with good humor, the responsibilities and sacrifices her choices have required of her," he continued. "I am grateful to her for the strengths she taught me by example."

Though she has now outlived him, Roberta once said her son liked to hold her up as an example of "what he hopes his lifespan will be."

John McCain also might have inherited his mother's sass, wit and rebellious streak.

He once answered the telephone to hear his mother say she was on a cross-country driving trip — by herself, in her 90s.

McCain wrote in his final book, "The Restless Wave," published this year, that his mother's "vivaciousness is a force of nature," but that although a stroke has slowed her once-brisk pace and has made speaking a "chore," she still has "a spark in her, a brightness in her eyes that would light up the world if she could resume her peripatetic life."

"Roberta is 106, but she's spunky," a close family friend told People magazine.

In February, McCain tweeted a video tribute to celebrate his mother's birthday.

"Happy 106th birthday to my wonderful mother Roberta – we love you mom!”

Granddaughter Meghan McCain also posted a tweet honoring her "incredible Nana McCain," and daughter-in-law Cindy McCain called her a "true inspiration."

Roberta was a vocal and energetic supporter of her son during his 2008 presidential campaign.

“Johnny is going to be the president of the United States and he’s going to keep the traditions … and the standards high,” she told a crowd of applause.

A native of Muskogee, Okla., Roberta Wright was nearly 21 and a college student in Southern California when she eloped to Tijuana, Mexico, in January 1933 with a young sailor named John S. McCain Jr.

He would go on to become a Navy admiral, like the father he shared a name with, and the couple would have three children — Jean, John and Joseph — within a decade.

McCain's mother raised the kids, with her husband away on Navy business most of the time. She didn't complain, and loved Navy life. The family lived in Hawaii and the Panama Canal Zone — where the senator was born in 1936 — among many points in between.

Roberta and her identical twin sister, Rowena Wright, who died in 2011, often traveled around the world together.

The Associated Press contributed to this report.