Hilary Duff has lost her four-legged best friend, Dubois. He was 10.

The actress, 30, announced the death of her Bernese Mountain dog on Instagram Monday with a heartbreaking tribute caption and her favorite video of him.

“I never let myself imagine what this day would look or feel like. It was us. And we were invincible. I am having to look into your beautiful amber almond shaped eyes and tell you goodbye today,” Duff wrote in her farewell message.

“Honestly I would take the pain of losing you 10x over to have had you for even a quarter of that time my dubie. First of all…thank you…for being my best friend…truly. You have been with me though true pain, true happiness and joy, true confusion and disappointment and all over again,” the mother of one continued.

Though she’s lost dogs in the past few years, Dubois’ death has been the most difficult. (Her Chihuahua named Coco died in February 2017, French bulldog Beau died in 2016 and Chihuahua Lola died in 2013.)

“You are more then I could have ever dreamt up on my own. I haven’t taken a step without you beside me for 10 years. You are my protector my comfort, my shadow, my understanding of all things good and warm and fierce,” Duff said in her tribute to Dubois.

“I can’t imagine this house without your noise, your love, your energy, your smile and wagging tail I know I will move into other parts of my life without you but I am scared. I have faith you will still be my shadow, my angel,” she continued.

Concluding, “There aren’t adjectives big enough to describe my love for you Dubes. My gratitude. I will miss you everyday of my life my sweet boy. You were that once in a lifetime dog. That special bond that not everybody gets. And I got you. You picked me. You were a force. You changed me forever. I will see you at the other end of the rainbow My boy. Forever indebted to you. Rip Dubois.”

Duff, who is a mom to 5-year-old son Luca, last shared a photo of Dubois on her social media on Feb. 1, posting a picture taken by boyfriend Matthew Koma.

In May, the Younger star announced she adopted a black Labrador mix puppy named Momo.