North Korea's leader Kim Jong Un described his relationship with US President Donald Trump as a "fictional movie," according to a new book by American journalist Bob Woodward that reveals correspondence between the two leaders.

The relationship between the two men was volatile, ranging from insults and threats of war, to a "declaration of love" by Donald Trump.

The famous American investigative journalist Bob Woodward obtained 25 "previously unpublished" messages exchanged by the two leaders, according to Simon & Schuster.

The house said, "Kim describes in the letters the relationship between the two leaders as deserving to be turned into a fictional movie, as they have an exceptional diplomatic relationship."

This book, titled "RAGE" (Rage), scheduled for release on September 15, is a continuation of "Fear: Trump in the White House" (Fear: Trump in the White House). The White House) published in 2018.

Donald Trump and Kim Jong Un met three times, and the first time was at a historic summit held in June 2018 in Singapore.

Despite this, the denuclearization negotiations in North Korea have not made any significant progress, rather they have stalled since the failure of the second summit in February 2019 in the Vietnamese capital, Hanoi.

However, this did not prevent the US President from praising his relations with Kim Jong Un. Rather, it went so far as to say that the two men "fell in love with each other."

"He wrote beautiful letters to me (...) we fell in love with each other," the US president told his supporters in September 2018.

Journalist Bob Woodward is known for revealing details related to the "Watergate" case that led to the resignation of President Richard Nixon in 1974.