Marston is a writer who writes under the name Marston Glenn, and apparently wrote a 'zombie book' called 'Bleed'. Marston also had a run-in with the law in 2012 when he was arrested for allegedly attacking his Playmate girlfriend Claire Sinclair.
Hefner's and Conrad's son, Cooper, often posts sweet photos of his grandmother, Conrad's mother, to social media showing they are close.
Hefner was born on April 9, 1926 ,in Chicago, Illinois, and went on to become a millionaire after founding the influential men's magazine in 1953.
On Wednesday night the official Playboy Twitter account announced: 'American Icon and Playboy Founder, Hugh M. Hefner passed away today. He was 91. #RIPHef.'
Hefner's death was confirmed in a statement from Playboy Enterprises that said he 'passed away today [Wednesday] from natural causes at his home, The Playboy Mansion, surrounded by loved ones'.
His son, Cooper Hefner, who is the chief creative officer of Playboy Enterprises, said: "My father lived an exceptional and impactful life as a media and cultural pioneer and a leading voice behind some of the most significant social and cultural movements of our time in advocating free speech, civil rights and sexual freedom.
"He defined a lifestyle and ethos that lie at the heart of the Playboy brand, one of the most recognisable and enduring in history.
"He will be greatly missed by many, including his wife Crystal, my sister Christie and my brothers David and Marston, and all of us at Playboy Enterprises."