A number of stars flocked to the comments section to congratulate Sylvia and Pete on their bub-to-be.
"Beautiful news. Congratulations," wrote Jesinta Franklin, while Sylvia's Today Extra co-host David Campbell added: "Best news ever!"
Tracey Grimshaw also sent her well wishes, writing, "Oh congratulations Sylvia and Peter. Outstanding production!"
Earlier this week, Sylvia revealed the couple's son Oscar was born via IVF. However it is not known whether fertility treatment was involved in the conception of their second son,.
"I know from my own personal experience of IVF that so much goes into having a successful embryo and having something sitting there that gives you the opportunity to make life for your family," Sylvia tearfully said during a segment about embryos.
"There's such an emotional attachment to those embryos, long before they become the baby or the child that you grow to love."
Peter, younger brother of Today star Karl Stefanovic, met Sylvia at work when they were put together for co-hosting duties on The Weekend Today Show.
He popped the question on holiday in France in 2016, getting down on one knee at a vineyard in Bordeaux.
In April 2017, they said their "I dos" in an intimate ceremony at Kangaroo Valley in New South Wales.
The pair weathered a difficult period towards the end of 2018 when Peter was axed from Nine following the Uber-gate scandal when he was overheard by an Uber driver whinging about the network and his colleagues with his brother Karl.