Delivering the defence’s closing submissions, Najib’s lawyer Tania Scivetti said any such letter would have had to pass through official diplomatic channels, which posed risks to the “sensitive” nature of the alleged donation.

“It might compromise the confidentiality of this gift,” she said, adding that the contribution from King Abdullah was personal and needed to be handled discreetly.

Scivetti told the court that Najib subsequently conveyed his gratitude to King Abdullah in person.

“He is always courteous, measured and respectful,” she said of her client.

In his testimony, Najib said he received US$20 million in 2011 from one “Prince Faisal”, whom he claimed was part of the Saudi royal household.

He admitted that he did not write to thank the then Saudi king or any other member of the royal household for the funds.

Najib said he did not want to engage in formal correspondence via Wisma Putra as the matter was sensitive.

The former prime minister is standing trial on 25 charges of abuse of power and money laundering over funds amounting to RM2.28 billion which were deposited into his AmBank accounts between February 2011 and December 2014.

The hearing continues tomorrow before Justice Collin Lawrence Sequerah.