But the two agreed to set aside their past differences and joined forces in an unlikely alliance to fight against scandal-hit former premier Najib Razak.
There is little doubt that royalty has readily concurred with his plan of action, one that reaffirms the truism that there are no permanent enemies in politics ~ "The king has indicated he is willing to pardon Anwar immediately", said Mahathir.
Under Malaysian law, Anwar is disqualified from running for office for five years after his release, unless he is pardoned by the King.
The royal pardon would mean he could return to politics straight away.
When Mahathir was Prime Minister the first time between 1981 and 2003, Anwar was his protege and deputy, tipped for the top job until Mahathir thought he was becoming too powerful.
Anwar was initially due to be released from prison in June. He has let it be known that he will assume power... only to hand it over to a "former apprentice" who was jailed after the two fell out and still remains behind bars.
Reporters and Anwar supporters were gathering outside a hospital in Kuala Lumpur where he is recovering from a shoulder surgery.
Mahathir said his four-party alliance will hold a meeting Saturday and name 10 ministers for a start.
"Whether Anwar will be part of the cabinet or not will be decided when the time comes", he said. He indicated this could include Attorney General Mohamed Apandi Ali, who was appointed after Najib sacked the then-attorney general in 2015 to escape possible prosecution over a corruption scandal involving the 1MDB state fund.
"In the case of foreign affairs, we want to maintain good relations with all countries regardless of their policies", he said.
It is unclear how long Mahathir will remain prime minister after Anwar's release.
"He, in fact, has hidden evidence of wrongdoing, and that is wrong in law". But he was also credited for transforming his Southeast Asian country from a sleepy backwater into a modern industrialised nation.
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