AceShowbiz - Former "Roseanne" favourite Martin Mull wasn't shocked when ABC bosses cancelled the show's reboot, insisting his TV boss has always had a problem keeping her thoughts to herself.

The actor, who played Roseanne's gay boss Leon Carp on the original show in the 1990s, has no qualms about what executives did after his former co-star published a racist tweet aimed at former Barack Obama aide Valerie Jarrett.

"I think they did what they had to do," Mull tells WENN. "My own dealings with Rosie never indicated to me anyone who would write that tweet (and) I certainly don't approve of the tweet. I never saw that in her, but I did see things in her that were inexplicable along the way; certain things I can't explain.

"I just say, 'That's Rosie!'"

Roseanne Barr recently apologised to Jarrett in a TV interview admitting she is "so sad" her tweet about the government aid was construed as racist.

In her first national television interview since the scandal, she told Fox News' Sean Hannity the social media post was a "political tweet" intended to address US-Iran nuclear policy and not Jarrett's ethnicity.

Hannity asked the comic to address Jarrett directly at which point the comic apologised to the former White House staffer, insisting she "never meant" to cause hurt. "I'm sorry you feel harmed," she added.

The disgraced actress had the revival of her television series canned by ABC bosses after she labelled President Obama's former adviser the product of the "Muslim brotherhood" and "planet of the apes having a baby".