Fitzy went on to reveal how his dog's condition suddenly deteriorated.
"It happened really fast, he hit a wall about 11, he wouldn't eat, he wouldn't move. I thought he's in a bit of trouble here. We found out he had a huge tumour in his stomach. I couldn't understand why BJ was so emotional, and I told her 'we have to be positive.'
"In the back of my mind I was just saying to myself 'it's just a dog, it's just a dog.' It didn't hit me until I got home because he's not annoying me anymore, I just wanted him to annoy me," Ryan explained as he burst into tears.
But the hardest part came when Fitzy had to tell his two young sons Hewston, eight, and Lennox, five, that Cooper wouldn't be coming home.
"I rang Hewie and I said mate he's pretty crook, I don't think he's going to make it. Hewie didn't know how to react so he puts the phone down and yells to Lenny: 'He's going to die!' and you just hear Lenny howling in the background, but that was their coping mechanism."
"I just want to say we need dogs more than ever at the moment because our place is a rabble you know, we don't talk about this on the show but homeschooling is stressful. I know a lot of families out there they don't even know if they're going back to work, it's horrible.
"I let me just say this, who is the one person always waiting at the door every time without fail with unconditional love? I want everyone to know don't ever take that for granted with your dog.
"In situations like this I bury myself, I have to work hard and I go and do a workout, sweat and listen to music. So I went onto Spotify to try and take my mind off things and I think I told you guys on the show that on Spotify you can do a pet playlist. So I put on there Cooper's playlist and there's a song on there that we used to play when we would go for walks, it's from the strokes. It's called Someday. Someday I'll see you again old boy, go chase those birds mate - I love you."
Ryan's powerful radio segment comes after he panned a touching tribute to Cooper just hours after his passing on Monday night.
"Lost the old boy Cooper today. Surreal feeling, it all happened so fast," the former Big Brother star began.
"Been thinking how important dogs are in the current situation we are all in. No matter how tough we are doing they are always there so happy to see you at home," he added.
"Don't take that for granted, it's been bloody tough coming home and realising he's not following you around. See ya old mate, now go chase those birds ❤️," Ryan signed off.
His post was accompanied with an album of beautiful photos documenting Cooper's life - from when he was just a fluffy young puppy playing with Ryan's young sons, to the day he and wife Belinda had to say goodbye.
In one heartbreaking photo, Belinda can be seen crying as she holds Cooper at the vet.
In another photo, a devastated Ryan can be seen cuddling his dog one final time.
Fitzy's upload was quickly flooded with well wishes from A-list names.
"So sorry to hear! Sending you all love," new mum Jasmine Yarbrough wrote.
"Oh mate. I'm so sorry. It's a loss that always hits you harder than you ever expect. Hope you and the family are doing ok," Dr Chris Brown agreed.
"Know the feeling well mate. Sorry," Home And Away actor Cameron Daddo added.