This Is Us star took to Instagram to share the heartbreaking news and gave her 4.4 million followers a look into the pooch's long life. "Last night, very unexpectedly, we lost our Joni girl. Yes, she was almost 13. Yes, she had pretty major surgery a week ago to remove a mass on her liver but she was recovering really well. Until last night," the "When I Wasn't Watching" singer wrote. "I knew something was amiss when she, lifelong food-obsessed, didn't finish her dinner and couldn't get comfortable in bed (despite being on pain meds). My mama intuition told me to bring her in and I'm glad we did." The 36-year-old, who is currently pregnant with her first child, continued, "I saw her puppy mug online way back in early 2008 and drove down to San Diego to meet her at @thebarkinglotrescue and was instantly smitten. I'll never forget the drive home, telling her that it was just us against the world now. To know her, was to love her. She never met a stranger. She was waaaaay more human (or muppet) than dog. She loved ANYTHING she could eat, even if sometimes it was gross (cat poop [sick emoji])." Mandy gushed about all of Joni's passions, from food, her brother Jackson and "lying in the sun to catch some zzzzs" to her husband Taylor Goldsmith, "her cats brother and sisters" and giving "very stinky kisses." "My heart is utterly shattered. She was my first love and best friend. Through every twist and turn of life of this past decade and change, she was right there," the star shared. "There's a deep chasm of emptiness that will never be filled but I am so grateful for her sweet nature and the endless connection, compassion, responsibility, patience and devotion that the love of a pet can bring into your orbit."