Orlando Bloom thinks his dog has died.

The 'Lord of the Rings' actor has spent the last week desperately searching for his beloved pet Mighty and after finding the pooch's collar, he's convinced his canine companion has passed away.

He wrote on Instagram: ''Mighty's on the other side now. After 7 days of searching from sunrise to sunset and into the wee hours, today, the 7th day ~the number of completion~ we found his collar...

''I have wept more this week than I thought possible, which has been very cathartic and healing...

''I left no stone unturned, crawled thru all the man holes, under the roads, searched every back yard and creek bed. Had two separate sniffer dogs do their best as well. I feel so grateful to have learned from my little Mighty man that love is eternal and the true meaning of devotion.

''I feel sure he was looking down on me whistling in every back yard and knowing that I was doing all I possibly could to respect our bond. He was more than a companion. It was a soul connection for sure. I'm sorry. I love you. Thank you. RIP my MIGHTY HEART my little fellow (sic)''

Orlando - who has nine-year-old son Flynn with ex-wife Miranda Kerr and is expecting a daughter with fiancee Katy Perry - revealed he's had the dog's name and a heart tattooed onto his chest above his heart in tribute.

Thanking those who had helped in the search alongside a video of him getting the inking, he posted: ''Thank you to the community for allowing me to search through their yards for him and supporting my midnight walks. It was reassuring to see the best of people even in the worst of times.

''To the angels of @dogdayssar I'm forever in your debt. You ladies are heaven sent.

''Lastly thank you to @scottcampbell for the ink. I love you brother (sic)''

Katy shared Orlando's lengthy post as she paid her own tribute to the pooch.

She wrote: ''We'll miss our little buddy boy, Nugget's brother so much. Forever a paw shaped hole in our hearts #ripmighty (sic)''