Dr Dre, 52, rose to fame with gangsta rap pioneers NWA in the 1980s, going on to found Death Row Records and more recently created the Beats headphone brand, bought by Apple in a multi-million-dollar deal.
In contrast Lee Hee-ho, the ageing widow of the late president known for his "sunshine policy" of engagement with Pyongyang, remains an influential figure in Korean politics even after her husband's death in 2009.
They make an unlikely couple, but were linked by an unidentified online user who posted on his blog in January that the former first lady was to marry the American rapper to "launder the late president Kim's slush funds".
The Seoul Western District Court on Friday dismissed the rumour as "groundless" and fined the 73-year-old man 5 million won ($4,400) for defamation.
"The defendant violated the honour of the deceased and the bereaved," Judge Lee Eun-hee said in the ruling, the Korea Times reported Monday.
"The rumour about the slush fund and the marriage between Lee and Dr Dre is groundless," the judge added.
But online South Korean commentators quickly picked up on the fictional wedding as one of the funniest jokes for some time.
"I cracked up just by reading the headline," posted one online user.
Another asked: "Will Eminem be singing at their wedding?"
