Phil Goff is standing by his comments about US President Donald Trump as he arrives back in New Zealand.

The former High Commissioner to the UK was sacked from his role after questioning whether Trump understood history.

Goff says Trump's treatment of Ukrainian President Volodymyr Zelenskyy prompted the question.

He told Mike Hosking the comments weren't made flippantly.

Goff says he thought about them seriously and wanted to know why the Trump administration was appeasing Russia.

He also acknowledges his comments were risky, but didn’t expect to be fired for them.

Goff says he thought the comments were close to the line, without crossing it.

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