Michelle and Barack Obama Mourn the Death of Beloved Dog Bo: He 'Was a Constant, Comforting Presence'

Michelle Obama/Instagram

Barack and Michelle Obama are mourning the death of their family dog Bo.

On Saturday, the former first lady shared the heartbreaking news that Bo had died at 12 years old.

"This afternoon was a difficult one for our family. We said goodbye to our best friend—our dog, Bo—after a battle with cancer," Mrs. Obama, 57, wrote on Instagram. "On the campaign trail in 2008, we promised our daughters that we would get a puppy after the election. At the time, Bo was supposed to be a companion for the girls. We had no idea how much he would mean to all of us."

"For more than a decade, Bo was a constant, comforting presence in our lives. He was there when the girls came home from school, greeting them with a wag. He was there when Barack and I needed a break, sauntering into one of our offices like he owned the place, a ball clamped firmly in his teeth," she added. "He was there when we flew on Air Force One, when tens of thousands flocked to the South Lawn for the Easter Egg Roll, and when the Pope came to visit. And when our lives slowed down, he was there, too—helping us see the girls off to college and adjust to life as empty nesters."

Mrs. Obama went on to reflect on how she "will always be grateful" that her daughters were able to spend "so much time together" with Bo before his death.

"This past year, with everyone back home during the pandemic, no one was happier than Bo. All his people were under one roof again—just like the day we got him. I will always be grateful that Bo and the girls got to spend so much time together at the end," she wrote.

"As a family, we will miss Bo dearly. But we are thankful that he lived such a joyful life full of snuggles, games of fetch, and evenings spent lying on the couch," she added. We also know we weren't the only ones who cared for Bo, and are grateful for all the love you showed him over the years. Please hug the furry members of your family a little closer tonight—and give them a belly rub from us."

RELATED: Celebrity Pets We Lost in 2021

Former President Obama also shared a loving tribute to the family's "true friend and loyal companion."

"For more than a decade, Bo was a constant, gentle presence in our lives—happy to see us on our good days, our bad days, and everyday in between," he wrote. "He tolerated all the fuss that came with being in the White House, had a big bark but no bite, loved to jump in the pool in the summer, was unflappable with children, lived for scraps around the dinner table, and had great hair. He was exactly what we needed and more than we ever expected.

"We will miss him dearly," he added.

The Obamas welcomed Bo into their family in 2009, shortly after Obama's first presidential inauguration. The canine was a gift to the couple's daughters, Sasha and Malia, from Senator Ted Kennedy, according to the Presidential Pet Museum.

Sunny, a female pooch, joined the family in 2013.

"Sunny is the perfect little sister for Bo — full of energy and very affectionate — and the First Family picked her name because it fit her cheerful personality," the White House said when Sunny was adopted, per the Presidential Pet Museum.

RELATED: Michelle Obama Shares Pics of Bo and Sunny on National Dog Day: 'I Love These Two Balls of Fur'

After the Obamas moved out of the White House in 2017, Bo and Sunny needed some time to adjust to living in a "regular" home, Mrs. Obama revealed while on her Becoming book tour in 2018.Surprisingly, one of the biggest adjustments was getting used to doorbells.

"Bo and Sunny were like, 'What's that?'" she told the crowd. "They're just now going to the door when the doorbell rings. It's taken them two years. It's the door, people are coming."

Never miss a story — sign up for PEOPLE's free weekly newsletter to get the biggest news of the week delivered to your inbox every Friday.

The presidential pets have made cameos in a number of family photos over the years.

In honor of Easter in 2019, the former president shared a family photo on Instagram that included Sunny and Bo, and back in 2016 he shared a sweet photo of himself giving Sunny some belly rubs for National Pet Day.

"With these two, every day is #LoveYourPetDay," Mrs. Obama wrote alongside another 2020 snap of the pets.