KUALA LUMPUR - Malaysian Prime Minister Mahathir Mohamad's rocky relationship with Johor's royal family was once again laid bare on Sunday (April 28) when he reminded the southern state's Crown Prince that the latter's post was "not permanent".

Responding to a recent jibe from Tunku Ismail Ibrahim, Tun Dr Mahathir said only Malaysians can remove him as prime minister.

"We need to remember the past when a crown prince had to abdicate and the position was given to his younger brother. That's the crown prince, a crown prince can be changed. Only the people can change the prime minister, not just anybody or someone who thinks he is big," he said at a press conference in Beijing that was streamed live over Facebook.

Dr Mahathir was in China to attend the Belt and Road forum.

"He thinks he is someone big, but he is just a small fry. If he thinks he's big, go and vote and bring me down," Dr Mahathir added in reply to a question regarding Tunku Ismail's recent remarks on a video.

In the video, Tunku Ismail was seen leaving Stadium Larkin in Johor after a football match in which Johor Darul Ta'zim went down 0-1 to Shandong Luneng in the AFC Champions League last Wednesday.

The vehicle ferrying him stopped when a fan shouted "Change Mora", in reference to the football club's coach Benjamin Mora.

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Tunku Ismail, who was seen in the front passenger seat, then put his head out of the window and retorted: "Instead of changing Mora, it's better to change the Prime Minister."

The relationship between Dr Mahathir and the Johor royal family became testy after Kuala Lumpur's retracted its decision to accede to the International Criminal Court (ICC) and on appointments to the state government.

The clash of these two giants following Malaysia's historic first-ever change of government a year ago was inevitable, given the Premier's low tolerance for royal interference, and the insistence by Sultan Ibrahim Sultan Iskandar and Tunku Ismail that their family remain sovereign over Johor.