Nikki Reed and Ian Somerhalder's beloved dog has died.

NIkki Reed with dog Ira

NIkki Reed with dog Ira

The couple are mourning the death of their pet pooch Ira after the gorgeous German Shepherd sadly passed away from cancer this week.

Taking to her Instagram account, the 'Twilight Saga: Breaking Dawn' star shared a sweet tribute message and uploaded a series of photographs of her beloved canine.

The 30-year-old actress wrote: "My sweet Ira girl. So many memories, so many adventures with you by my side. You've been my best friend for so long, and as I sit here and write you this letter, I still don't know if I am able to say goodbye.

"You are the definition of unconditional love my gorgeous girl. You taught me so much about so many ways our greatest teacher.

"You showed me that sitting on my toes felt as sweet as holding hands, and you knew what I was thinking before I even said it. I still cant figure out how all 75 pounds of you could curl up into such a tiny ball at my feet. I guess you'll have to explain that trick to me in our next life together.

"We shared so many secrets, so many laughs, so many tears. You know it all, you've seen it all. You brought smiles to all of us in our saddest moments, touching hearts everywhere you went, and there isn't a single person who didn't say you were magic my girl. Everyone who met you fell in love, everyone who met you wanted more. Thank you for being my kid in this life my Ira girl. Ill be bringing you back to our favorite lake soon... (sic)"

The couple - who have many pets as they foster animals looking for permanent homes - shared memories of running and holidaying with Ira, along with photos of her joining them on paddle boarding trips and curled up asleep on their bed.

Nikki admitted she and the pooch had shared "water bottles and kisses".

'The Vampire Diaries' star Ian, 39, wrote: "At 12:11 PM PST this beautiful girl took her last breath. Quietly cancer had filled this amazing girl of mine and there was nothing any of us could do. I've never known a more incredible animal. A soul that spoke 1,000 languages. Kid, I will miss you and anyone that ever got to know you will miss you. I love you kiddo. Love, Dad. (sic)."

As well as their family of pets, Nikki and Ian have 10-month-old son, Bodhi.