The heartbreaking letter Steve wrote when he 32 was uncovered in 2016. In it, Steve thanks his parents for their strength, and how they raised him.
"At 32, I am finally starting to figure it out. In good times and in bad, you were there. Your strength and endurance to raise me will not go unrewarded. My love for you is my strength!
"For the rest of my life I will reflect on the unbelievably GREAT times we've shared and will continue to share. You're my best friends!"
Irwin, who signs off with a thank you, was to find even more joy with the birth of his daughter Bindi four years later, followed by son Robert.
Bitter family feud explodes
Fast-forward to today, and Bindi Irwin insists her grandfather has never had anything nice to say to her, and is not part of their lives whatsoever.
Bindi made the unsettling allegations against her grandfather in her Father's Day post last weekend (Father's Day outside of Australia was June 20), dedicated to her own father, her husband, Chandler Powell, and her father-in-law. Irwin was asked why she left Bob out of the tribute, and the 22-year-old new mum did not hold back with her response.
"Unfortunately my grandfather Bob has shown no interest in spending time with me or my family," she wrote, according to 7News.
"He has returned gifts I've sent him after he opened them, he has ignored my correspondence and from the time I was a little girl he has ignored me, preferring to spend time doing anything else rather than being with me," Bindi wrote.
"He has never said a single kind word to me personally. It breaks my heart but it is not healthy to engage in an abusive relationship.
"I hope everyone remembers to be kind to one another but most of all care for your own mental health," she added.
"I have struggled with this relationship my entire life and it brings me enormous pain."
Shortly after, family members hit back at the claims, along with Bob's biographer and good friend who used to work at Australia Zoo, Amanda French.
Family hit back: 'The lies need to stop'
Another member of the Irwin family, Bethany Wheeler, angrily disputed Bindi's claims in a Facebook post of her own, defending Bob or "Poppy" as she affectionately calls him.
Bethany explained she is "the granddaughter of Bob Irwin via marriage of my father and my Stepmother Mandy as a very young child," and called Bob "the most genuinely beautiful human on this planet and has NEVER spoken out or put down anybody! He is a man who sits silently and battles his demons alone, in what is great sadness. He doesn't retaliate, only prays for his grandchildren's safety and good lives."
Wheeler wrote that her "sisters and brothers will happily back me up when I say that Bob Irwin is a passive and beautiful human and these lies need to stop".
Bob Irwin's biographer also came to his defence, saying she had been "devastated" by Bindi's claims of abuse.
Amanda French, who co-wrote Bob's 2016 autobiography The Last Crocodile Hunter, spoke to Brisbane radio showStav, Abby and Matt expressing her sadness over the comments made by Bindi.
According to Amanda, Bob resigned from Australia Zoo in 2008 and hasn't seen the kids since.
"It's a surprise with what Bindi came out and said. There were some pretty weighty terms that were thrown around, psychological abuse and all that stuff. You'd have to have some pretty big evidence to back that. It's a pretty big call to make," she said.
What happened between Bob and Terri Irwin after Steve's death?
According to Amanda, she says Bob will take what happened between him and Australia Zoo it to his grave, but has alluded to how management changed when Steve died.
"He's maintained a very neutral position about it [resigning] even when he published his autobiography.
"The reason why he did that is because he knew there would be consequences for Australia Zoo. He didn't see eye-to-eye on issues to do with Australia Zoo at the time and some of the animals."
Interestingly, Amanda did confirm that Bob had returned gifts sent from the family, which is something Bindi said, but admitted they were only ever sent from Terri, not the kids, and that they were incredibly "strange".
"I've been there when he's received gifts, and it was a shower cap. Really strange thing to send a man. To me it's a passive aggressive thing to do, that's my perspective. After a while of that Bob returned one of the gifts."
One sticking point for Amanda was Bindi's comments about how her family has maintained financially supporting Bob, despite having no relationship with him.
"He gave them that zoo," Amanda said, reminding everyone that it was gifted to Steve and Terri when they got married. "There was always an agreement that he would be on a pension and looked after."
Bob cannot visit Steve's burial site
The worst part for Bob in Amanda's eyes is the fact that his son Steve's burial site is on the zoo, somewhere he cannot go to visit.
"It's hard for him not to be able to return to his son's resting place, as you can understand. He hasn't been back to Australia Zoo since the wildlife hospital was launched in 2008. It was supposed to be dedicated to Bob and his late wife Lyn, because that was where Lyn did the bulk of her wildlife work.
"They retracted Bob's invitation to attend that launch and he turned up anyway. I organised that event and I remember him turning up on the day and sitting in the audience looking very upset."
Amanda claimed that many staff members have left the zoo while it has been under Terri's management, citing similar issues to Bob.
"When I went back to write the book and spoke to those key people who worked with Bob and Steve, there was still some bad blood there with how they were treated. They adored them [Bob and Steve], and never had a boss like them again."
While writing the book, she admits that Bob tried to send his grandchildren letters, but was unsure whether or not they were receiving them because they went through so many people at the zoo, "so we decided to close off the book with a message to his grandkids".
She notes that it would be hard for Bob to get in contact with his grandchildren without Terri being involved.
What's next?
In the wake of the subsequent media storm, Bindi announced she would be "taking a break" from social media in the interest of preserving her mental health.
"I'm taking a break from social media and most of my work in the public eye for a month to be with my beautiful daughter and my wonderful family," she wrote on Instagram.
"I feel tremendously grateful to share our life and conservation work with you but I need some time to focus on the happiness that is my family (both human and animal)."
Bindi – who also posted a quote to social media about "how much strength it takes to pull yourself out of a dark place mentally" – also thanked her followers for "sharing and speaking your truth".
Hours later, her husband Chandler shared a post of his own expressing his support for her.
"You inspire me with your unwavering kindness and your ability to stand up for what is right," his post read.
He shared the same photo that featured in Bindi's earlier post about taking a social media hiatus.
"You are the strongest and most beautiful person inside and out," he wrote.
"Grace has an amazing mama to look up to."
Terri went on to upload a vague, cryptic post on social media.
Irwin shared a post on Twitter about "avoiding certain people" just days after the family's feud made headlines.
The full quote is by author and military veteran Steve Maraboli, and reads: "Avoiding certain people to protect your mental health is not a weakness … It's wisdom."
The mum-of-two captioned the snap: "Thank you @SteveMaraboli. Another jewel. Caring for others seems to be easier than caring for ourselves. It takes courage to follow through on what we know is the right thing to do. Wishing everyone the best to be brave and wise. It's worth it!"
