Elon Musk's father Errol Musk took a jab at his billionaire son during an interview with Australia's "Kyle and Jackie O Show," telling the hosts he is not "proud" of him because the Musk family has "done a lot of things for a long time."

"It's not as though we suddenly started doing something," he said. "I mean, the kids were traveling around the world with me when they were tiny, and they've been doing pretty much very interesting things… but Elon has really surpassed the mark."

Musk's father went on, sharing that the billionaire business magnate is not as happy as he would like to be and that he believes his successes came years too late.

"[Elon] sometimes feels that he's an underachiever. He feels that he's behind schedule," he added, also sharing that the Musk family has adopted the mentality as a whole.

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Elon Musk

Tesla CEO Elon Musk in June. (AP Photo/Kiichiro Sato, File)

Musk went on to discuss Elon's younger brother Kimbal, who he claims is also a billionaire but falls short of his brother's estimated net worth of $260 billion.

"He's my pride and joy, Kimbal," he said.

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Musk characterized both of his sons as "stoic" and "icy" during the interview.

Elon Musk

File photo - Tesla Motors CEO Elon Musk talks at the Automotive World News Congress at the Renaissance Center in Detroit, Michigan, Jan. 13, 2015. (REUTERS/Rebecca Cook)

"Kimbal has managed to find a girl… she [Christiana] goes with him everywhere, and so he's very fortunate and it makes me very happy."

Musk then relayed his concern for Elon since he lacks a substantive relationship similar to the one his brother has, questioning whether Elon could ever find a woman willing to sacrifice her career for him.

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"If he meets a girl that's sort of similar to him, she's probably got masses of program things to attend to as well, so they can't spend time together," he said.

"He has to find a woman who's prepared to give up what she's doing and that's not easy."

The SpaceX, Tesla and Neuralink CEO sparked controversy in April when he purchased tech giant Twitter, pushing back against the platform's allegedly anti-free speech policies that favored leftist viewpoints, but the deal is in jeopardy as Musk seeks to pull out of the purchase.