The blonde beauty has kept her son Xander's paternity a secret since falling pregnant in 2011, but reports linking the two X-Men alumni have continued to circulate, much to Marsden's annoyance.
In a new interview with Playboy magazine, he says, "There's so much stupid talk out there. I think that came from somebody thinking we were both in X-Men, so it must be true."
However, Marsden admits the two stars have learned to laugh about the false baby claims: "Every time I see January, she's like, 'Hey, father of my baby.'"
Jones starred as mutant Emma Frost in 2011's movie prequel X-Men: First Class, while Marsden featured as Scott Summers and his alter ego Cyclops in the original X-Men film, which was released in 2000, and its two sequels, X2 and X-Men: The Last Stand.
The actor is already a father of three - he has two children with his estranged wife Lisa Linde, while he welcomed a boy named William Luca last December (12) following a brief fling with Brazilian model Rose Costa.