Karl Stefanovic's 18yo son has reportedly taken on his mother's surname on social media.

Karl Stefanovic’s oldest son no longer goes by his father’s surname, instead – on Instagram at least – adopting his mother’s surname in the wake of his parents split.

According to screenshots obtained by The Daily Mail, Stefanovic’s 18-year-old son Jackson reportedly changed his Instagram handle to Jackson Thorburn on Instagram.

However, it appears he has since changed it once again.

Rumours of a frayed relationship between the Today Show host and his oldest child first came to light after unconfirmed reports emerged following the 43-year-old’s commitment ceremony to his 34-year-old fiancé Jasmine Yarbrough, where it was believed Jackson did not attend.

As noted by The Daily Mail, it is so far unclear when the 18-year-old changed his Instagram handle, though in the past, when tagged in his father’s pictures, he was using the Stefanovic name.

On footy night I prefer no fuss moose in the hair. @jackson_stefanovic loves a soft blow wave.

A post shared by karl stefanovic (@karlstefanovic_) on Jun 25, 2016 at 1:57am PDT

In October 2016, Stefanovic announced his split from his wife of more than two decades, Cassandra Thorburn. The two share two other younger children, 12-year-old daughter Ava and 11-year-old son River.

Meanwhile, 2GB host Ben Fordham has announced he will be stepping in to the Today Show role for next week while Stefanovic is on leave.

Posting on Twitter, Fordham said: “I’m hosting the Today show this week with this awesome human. Tune in.”

What Peter and Karl Stefanovic should realise about venting in an Uber… post continues after audio. 

Last month, Woman’s Day reported both Channel 9 and Stefanovic had an “exit strategy” prepared for the Today Show, with the magazine claiming the 43-year-old will be gradually phased out before being permanently replaced by fill-in host Ben Fordham next year.

In an interview with News Corp in the wake of Uber-gate, TV Tonight editor David Knox told news.com.au Fordham is a legitimate contender for taking the Today Show job when Stefanovic eventually tires of the role.

“Nine already has Ben Fordham earmarked for the [Today] job and the ratings with him in the chair have not gone down,” Knox said. “They went up.”