Amber Heard pokes fun at Australian deputy PM over citizenship

It was a free shot that proved too irresistible to pass up.

When Australian Deputy PM Barnaby Joyce was revealed to be a New Zealand dual citizen on Monday - possibly in violation of constitutional rules - social media users joked about what Amber Heard and Johnny Depp might think.

The actors were famously targeted by Mr Joyce for breaking rules of their own: failing to declare their dogs, Pistol and Boo, to Australian officials in 2015.

Mr Joyce had threatened to have the dogs put down, prompting Heard and Depp to release a stilted apology video for defying the biosecurity laws of Australia - which they called "a wonderful island".

The saga made headlines around the world and was widely enjoyed online, where it was dubbed the #WarOnTerrier.

So it was probably no surprise that Mr Joyce's citizenship trouble - which is bound for Australia's High Court - generated clamour of its own.

During the debate over the dogs, Mr Joyce stressed that the actors would not receive special treatment because of their high profile, and must obey the law.

"The consequences of a disease outbreak could have been terrifying," he wrote when sharing the pair's apology video on his Facebook page.

Last year, Heard avoided a conviction after pleading guilty to making a false statement on her immigration card.

On Tuesday, she chimed in on Mr Joyce's difficulty - to effectively have the last laugh.

"When @Barnaby_Joyce said "no one is above the law" I didn't realize he meant New Zealand law ..." she tweeted.

Her tweets were well shared, receiving both applause and criticism.

Perhaps unsurprisingly, Mr Joyce has not responded.

Barnaby Joyce's eligibility for office will be tested by Australia's High Court