Speaking with the public broadcaster ahead of his 70th birthday on Saturday, the King said he was asked by Prime Minister Stefan Löfven to write a letter to Saudi King Salman Abdul Aziz in an effort to ease the tensions between the two nations.
The row between the two countries began back in early spring 2015 when Sweden's Foreign Minister Margot Wallström told parliament that Saudi Arabia was a "dictatorship" that violated human rights. Sweden also announced that it would not be renewing a long-standing military cooperation deal between the two countries.
Saudi Arabia later recalled its ambassador and froze Swedish business visas to the country.
Although the exact wording of the letter is unknown, the King said it helped thaw out the frosty relations. He told Swedish Radio it was his duty to help out when asked.
"There is a close cooperation with the current government. It is obvious that we work together on foreign policy issues. So, it was just fun," he said.
In Sweden, the monarchy has no formal political powers and the King’s role is that of a ceremonial and representative nature.