Skinner, 54, and Dennis, 57, starred in the BBC sitcom as beleaguered couple Sue and Pete Brockman, who are constantly outsmarted by their three children Jake (Tyger Drew-Honey), Ben (Daniel Roche) and Karen (Ramona Marquez), from 2007 to 2014.
The pair are thought to have started dating in 2017 after splitting from their respective partners.
Dennis separated from wife Kate Abbot-Anderson in 2015 while Skinner reportedly broke up with husband Charles Palmer, a director, in 2016.
TV presenter Lorraine Kelly congratulated Skinner on the new relationship as the actress appeared on today’s edition of the ITV show.
“And of course you two are together, I didn’t even know that!” Kelly said. “That’s brilliant, congratulations.”
“It’s a lovely little life surprise, isn’t it?” Skinner replied.
The host then joked that “if you know somebody really well, it cuts down all of that going out on the first date malarkey,” adding: “You know what his favourite colour is and you know whether they like brown sauce.”
“Absolutely, we can just move on,” Skinner said, before describing her relationship as “a lovely thing.”
In an interview with The Times published earlier this month, the actress revealed that “nobody really noticed” when she and Dennis first started dating.
“People said to us that someone will notice soon but I kept telling them, ‘We’re both over 50. Why would anyone be interested in that?’” she told the paper.
“We’ve got families we wanted to protect, but everybody’s pretty cool and happy with it.”
Dennis previously told the Mail on Sunday that he and his partner are “so very happy.”
Skinner has two sons with her marriage to Palmer, while Dennis shares a son and a daughter with Abbot-Anderson.
Lorraine airs weekdays from 8.30am on ITV.