Malaysian Prime Minister Mahathir Mohamad and the Johor crown prince Tunku Ismail Sultan Ibrahim have recently engaged in a war of words over the powers of the constitutional monarchy to interfere in political matters such as Kuala Lumpur's now-retracted decision to accede to the International Criminal Court (ICC) and on appointments to the state government.
Johor ruler, Sultan Ibrahim Sultan Iskandar, has also exchanged words with the Malaysian prime minister.
The testy relations between Tun Dr Mahathir and Johor's royal family date back to the early 1990s, during the 93-year-old leader's first period in office when the government removed immunities enjoyed by the Malay rulers following episodes of assault by Johorean royalty.
Here is a timeline of the recent spat.
April 5: Dr Mahathir said Malaysia will withdraw from ratifying the Rome Statute of the International Criminal Court.
The announcement came hours after Selangor Umno said it will be sending a memorandum to the state's Sultan on the matter, claiming that acceding to the Statute will affect the sovereignty of the country's Malay Rulers.
"There seems to be a lot of confusion about the Rome Statute, so we will not accede," Dr Mahathir told Malaysian media.
"This is not because we are against it, but because of the political confusion about what it entails, caused by people with vested interests."
In March, Tunku Ismail tweeted that the government had failed to consult the Conference of Rulers when it agreed to accede to the Rome Statute.
The government's decision, he said, undermined the rulers' position.
Sultan Ibrahim also accused Putrajaya of violating the Federal Constitution by signing the Rome Statute.
In response, Dr Mahathir said on March 24 that only the good provisions would be accepted from international treaties such as the Rome Statute.
April 9: Dr Mahathir said that Tunku Ismail was not above the law.
He said the prince was free to criticise the Pakatan Harapan government as long as no laws were broken.
"If there are statements that are deemed seditious, we will take action against him. He is not above the law," he told reporters at the Parliament lobby.
On the same day, Dr Mahathir told the media that Datuk Osman Sapian had tendered his resignation as Johor's Menteri Besar on April 8.
In response to Dr Mahathir, Tunku Ismail said he was ready to face any criminal action if he had indeed made any seditious remarks.
"Sila (please do). If I have to go down for upholding the Constitution, the Malay rulers and Islam. By all means. You know where to find me," he said in a tweet. "Like a normal citizen, I have the right to ask questions and give my opinion. I'm all yours. Finish what you start."
April 10: The role of appointing the new Johor Menteri Besar lies with the party that won the election, not with the Sultan of Johor, said Dr Mahathir.
When pressed if it was the Sultan of Johor who would be appointing the Menteri Besar, who heads the state government, Dr Mahathir said: "This is a political decision."
On the same day, Sultan Ibrahim said he wants "certain quarters to stop making noise and fighting about politics and focus on efforts to take care of the nation instead".
He posted on Facebook: "On matters concerning Johor, do not try to meddle in state affairs as this is a sovereign state that still has a Sultan. I will make the best decision for the people when the time comes."
April 11: Dr Mahathir responded to the Sultan's statement from the day before by mocking the idea of the state's sovereignty.
He told the press: "I believe Johor is a part of this country, unless of course it's a foreign country. I don't interfere in internal affairs of foreign countries."
April 14: Sultan Ibrahim said that the federal government should stop "wasting time" talking about who has the authority over Johor, in a clear reference to Dr Mahathir.
In a statement on Facebook after the swearing in of Johor's new Menteri Besar, the 60-year-old ruler said: "I would like to advise the government to stop wasting time by talking too much about non-beneficial things, slandering and creating stories just to attract attention or to confuse the rakyat.
"Instead, focus your attention on assisting the people's welfare and improving the country's economic development."
He added: "The Johor government has long been established, where it has its own culture and way of administrating itself.
"Those on the outside do not have to start talking about who has the power and how to administer the state."
April 22: At a hastily convened meeting of Dr Mahathir's Parti Pribumi Bersatu Malaysia, top party leaders said that Dr Mahathir had felt slighted by how the new Johor state cabinet line-up was selected.
The party's supreme council member Kadir Jasin also said the cabinet had a "general understanding" that there would not be a reshuffle of the state cabinet despite Dr Sahruddin Jamal's appointment as Johor's new Menteri Besar.
April 24: In a blog post, Dr Mahathir reminded the public that it is the government that has the last say on who is Menteri Besar and not the constitutional monarchs.
He listed the events that led to the adoption of the country's Federal Constitution, where it was agreed that Malaya - and later Malaysia - would be a democracy where the people would choose its government.
Tunku Ismail posted excerpts of the Federal Constitution on the rights and powers of the Rulers on his Facebook page on the same day.
He cited Article 71 (1) which states that the "Federation shall guarantee the right of a Ruler of a State to succeed and to hold, enjoy and exercise the constitutional rights and privileges of Ruler of that State".
April 24: 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.
The vehicle ferrying him stopped when a fan shouted "Change Mora", in reference to the football club's coach Benjamin Mora.
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."
April 25: Sultan Ibrahim said he hoped that with the appointment of Johor's new Menteri Besar, Dr Sahruddin, as well as state executive councillors, any misunderstanding or disputes between the state and federal governments would be set aside.
"I hope all quarters will give their full cooperation to ensure the administration runs smoothly," Sultan Ibrahim wrote on his official Facebook page.
He added that the state leadership should work together and double their efforts to help the people. "It is better that we meet and discuss this in a mature way for the benefit of everyone - especially the people," he said.
April 28: 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.
"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 remarks in a video.
May 1: The Raja Permaisuri of Johor, Raja Zarith Sofiah Sultan Idris Shah, the mother of Tunku Ismail, leapt to his defence after Dr Mahathir's fierce exchanges with the Johor royalty in recent weeks.
She said in a Facebook post, that she could not bear to see Tunku Ismail being showered with criticism from all quarters after his comments that his father, Sultan Ibrahim, has absolute authority to choose the state's Menteri Besar.
In response to the post, the crown prince comforted his mother. "Don't worry Mama. Everything is going to be alright. No matter how dark the storm may be, there will always be sunlight. I Promise you. Allah Peliharakan Sultan," he said in a Facebook post.
May 6: Dr Mahathir called the crown prince "a little boy" and "stupid", following weeks of angry exchanges between the two and Johor ruler Sultan Ibrahim Sultan Iskandar.
They had argued back and forth on whether under the Constitution, the federal government or the royal family has the ultimate right to administer the state government and appoint top state officials.
Speaking in a media interview in Putrajaya, Dr Mahathir, 93, said Tunku Ismail, 34, should stop commenting on matters beyond his knowledge, Malaysiakini reported Dr Mahathir as saying.
"I don't want to comment on the sultan because if I say anything that is not good, it's not nice because he's the sultan," Dr Mahathir was quoted as saying.
"But this TMJ (Tunku Ismail) is a little boy… He is stupid because he doesn't know what is happening. So don't talk. When you don't know anything, don't talk," the premier said.
Tunku Ismail is widely referred to in Johor as the TMJ, short form for Tunku Mahkota Johor or Johor's crown prince.
Dr Mahathir's remarks on the crown prince was made when he was asked to comment on Tunku Ismail's statement that his father's good deeds, such as giving land to the people and government, were not highlighted.
Tunku Ismail's lament was made following the surprise revelation that a plot of federal land earmarked for the Johor Baru-Singapore Rapid Transit System (RTS) rail link had been quietly transferred to Sultan Ibrahim.
The ruler had said through his aide that he was not aware of the transfer, and has said he is prepared to surrender the land back to the government without cost if the RTS project is immediately carried out.
May 6: Dr Mahathir’s special media adviser Datuk A. Kadir Jasin called upon the authorities to probe taxes paid by Mados Sdn Bhd, a company believed to be linked to the Johor royalty.
He said that new Inspector-General of Police Datuk Seri Abdul Hamid Bador should reopen some "frozen" and "closed" investigation papers but did not elaborate.
He also said the Inland Revenue Board should probe Mados. The company is said to be owned by the Johor royal family.
"The little boy has asked us to do 110%, but I think 50% is enough," Datuk Kadir wrote in a Facebook post on May 6.
His post came after Dr Mahathir said the Crown Prince of Johor is a "little boy who does not know anything".
Mr Kadir also warned that "Little Boy" is like the atomic bomb that destroyed Hiroshima in 1945.
"It is very dangerous although it is small and does not know anything. So we have to do something, not just talking," he said.