Earlier this month, model Michael Girdenti claimed he was Mason's dad and even released pictures of himself as a child to show the apparent similarities.
But this rumour has finally been put to bed as the results of a paternity test have been obtained by E! News.
"After three-and-a-half years of rumours and lies being spread by an individual I met briefly at a photo shoot, I am setting the record straight that Scott is Mason's father," said Kourtney.
"While it saddens me to have to address these ridiculous lies - especially when the truth was never in doubt - this story must be put to rest."
It seems Girdenti was pretty convinced he was the toddler's father and even filed a paternity case against Kourtney asking for joint custody of Mason.
"After [Mason] was born, and I saw the photos of him, I began to wonder," he told In Touch magazine. "I would definitely want to acknowledge Mason if he's my kid - he deserves to know his real father."