Sir John Key on receiving Australia's highest honour

It's only been a month since he got his knighthood, but Sir John Key's already got a new accolade.

This time he's receiving Australia's highest honour, becoming a Companion of the Order of Australia.

It's their equivalent of a knighthood, and he's only the 5th Kiwi ever to receive it.

Mr Key has been praised for helping build the Trans-Tasman relationship through security and economic growth.

The former Prime Minister says the honour belongs to the whole country.

"I very much feel it's been bestowed on New Zealand," he told Newshub. "It's a reflection of the Anzac relationship."

He had to work with Australia's revolving door of leaders during his term as Prime Minister: Kevin Rudd, Julia Gillard, Mr Rudd again, and then Tony Abbott.

But it was his relationship with current Australian Prime Minister Malcolm Turnbull that eclipsed them all.

He recommended Mr Key receive the Honour, calling him a "great friend" of Australia - so great, in fact, that he sent a text when Sir John retired, saying: "say it ain't so bro".

"[There has] always been a bond there and I've enjoyed his company. It's no secret I'm a great supporter," Mr Key says.

The bromance resulted in a deal last year to give Kiwis a path to Australian citizenship for the first time since 2001.

But Mr Key is still pushing for more to be done.

"Actually I think there's a very strong case why Australia will have to change that."

A pursuit that today carries more weight than ever, as the weight of his accolades continues to grow.