Jimmy Carter, the longest-living US president, turned 99 on Sunday, defying the odds seven months after entering hospice care to notch another birthday.

World leaders, celebrities, and everyday people sent wishes to the almost-centenarian, while the White House displayed a giant wooden cake on its lawn with 39 candles for the 39th president.

"I admire you because you have such incredible integrity, character, and determination," US President Joe Biden said in a video message posted on X, formerly Twitter. "God loves you, happy birthday pal."

Carter, who already beat brain cancer in his 90s, was thought to be on his last legs in February when his nonprofit foundation, the Carter Center, announced he would spend his "remaining time" at home with his family in the small town of Plains, Georgia in hospice care.

Since the announcement, Carter, a Nobel peace laureate and former peanut farmer, has been reported to be sleeping a lot but also still watching baseball and eating his beloved peanut butter ice cream.

Last weekend he even made an appearance at the Plains Peanut Festival, riding in the parade next to his 96-year-old wife, Rosalynn.

Carter's grandson Jason Carter told USA Today last month that the couple was "coming to the end, as we know," but that "they're both doing as well as can be expected."

"They are together. They are at home. They're in love, and I don't think anyone gets more than that. I mean, it's a perfect situation for this time in their lives," he said.

Carter's presidential library in Atlanta bumped a celebration for the ex-president one day early to Saturday, as the specter of a federal government shutdown — avoided at the last minute — threatened to ruin the festivities.

In this universe or the next

The Carter Center, also in Atlanta, said it had received more than 15,000 birthday messages for the president, which it compiled into a digital mosaic.

Willie Nelson, Jane Fonda, former president Bill Clinton, and astrophysicist-author Neil deGrasse Tyson were among those to weigh in.

"99 trips around the sun — congratulations. If you do the math on that, that's nearly 58 billion miles," deGrasse Tyson said. "May you have many more such trips around the sun, in this universe, or the next."

In May, the Carter family announced that Rosalynn had dementia, and said it hoped that revealing her condition would help lessen the stigma that surrounds it.

At 77 years, the Carters' marriage is the longest in US presidential history, eclipsing the 73 years of former president George H.W. Bush and his wife, Barbara.

Carter served one term as president after being elected in 1976 on the heels of the Vietnam War and the Watergate scandal. His presidency included successes like the Camp David peace accords, but also controversies such as the Iran hostage crisis.

He dedicated his time in retirement to humanitarian affairs and founded the Carter Center, which promotes human rights and conflict resolution.