The person who will be missing from Bindi Irwin's Sweet 16th.

They are one of our most famous families. But a rift has kept them apart for six years.

Bindi Irwin is holding a massive 16th birthday bash at Australia Zoo on July 24. While thousands are expected to attend, Bindi’s grandfather, Bob Irwin, will not, choosing instead to be in far north Queensland to work on a crocodile conservation project.

In 2008, 18 months after Steve Irwin's fatal stingray attack, Bob Irwin resigned from Australia Zoo and The Guardian reported the first sign of the family rift. "There are people at the zoo who think that Steve's commitment to animal research and conservation isn't being maintained," one zoo volunteer told the Guardian. Bob's resignation was attributed to a dispute between him and Terri Irwin (Steve's widow).

According to rumours, Bob accused Terri of commercialising the family's empire. While he wanted to maintain a strong conservation focus. 

Then in 2010, Bob spoke to Woman's Day after a near-fatal heart attack. “I haven’t heard from [Bindi and Robert] and it is sad, but that’s a part of life I guess,” he told Brisbane’s Sunday Mail. “Of course I’d like to see them but [the rift with Terri] hasn’t been resolved.”

And it seems the rift continues with his refusal to join in Bindi's festivities.

Bindi has asked guests of her massive bash to wear animal onesies and plans to entertain with contortionist acts, rock climbing, African drumming and hula hooping workshops at her party.

An Australian Zoo spokeswoman neither confirmed or denied whether Bob had even received a direct invitation. Instead telling Ninemsn, "I’m not sure why Bob is not attending."

After her public birthday party, Bindi, who's currently studying Business and Tourism at TAFE, wants to have a quiet party with her immediate family and "some Chinese Food". 

CLICK THROUGH the gallery to see all the pics of Bindi growing up:

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This is about to become the most amazing birthday cake – EVER.

Is my mum normal? She wants to be paid to look after her grandkids.