Kate Middleton and Prince William send heartfelt message to world leader that supported them through Queen's death

Kate and Prince William have penned a heartfelt message to outgoing New Zealand Prime Minister Jacinda Ardern.

The Prince and Princess of Wales tweeted: "Thank you @jacindaardern for your friendship, leadership and support over the years, not least at the time of my grandmother’s death.

"Sending you, Clarke and Neve our best wishes. W & C."

Last week Ardern announced she would be standing down as Prime Minister and Labour leader eight months before New Zealand's national elections.

She said: “I’m leaving, because with such a privileged role comes responsibility – the responsibility to know when you are the right person to lead and also when you are not.

"I know what this job takes. And I know that I no longer have enough in the tank to do it justice. It’s that simple.”

She added: “I am human, politicians are human.

"We give all that we can for as long as we can. And then it’s time. And for me, it’s time.”

This month the Prince and Princess of Wales have remained silent on the multiple attacks fired at them in Prince Harry's autobiography Spare.

Kate's popularity has dropped more than Meghan Markle since Prince Harry began launching his attacks on the Royal Family.

In a further blow to the Firm, Prince William's popularity has dropped more than Prince Harry's since Spare was released on January 10.

However, the Prince of Wales remains overall more popular than his brother.

In a poll from Ipsos Mori, Kate's popularity dropped seven points whilst Meghan lost only five points.

Prince William has seen a decrease of eight percentage points whilst Prince Harry has suffered a drop of seven per cent.

Prince William and Kate remain the most popular royals, with ratings of 61 per cent and 60 per cent respectively.

Whilst just under 70 per cent think the Prince of Wales will be a good king.

Ipsos interviewed 1,000 people aged between 18 and 75 in the UK on January 10 and 11.