The 53-year-old actress, who plays Nessa Jenkins on the hit comedy, met her husband David Pete almost 20 years ago.
But at the time he was apparently happily married with three teenage children.
The pair first crossed paths while they were working on a BBC comedy pilot together – which saw David leave his wife and start a relationship with Ruth.
The happy couple have been together since and now share a home in Cardiff.
When promoting her new novel Never Greener last year, Ruth did admit the pair had an affair.
At the time she insisted: “Nobody in the book is based on anybody in my life.
“Of course you have to ask. But my imagination is quite ferocious, in that I can imagine the worst possible scenarios.
“Affairs cause a lot of pain, they’re not something one aspires to do. You don’t aspire to cause pain to people in their life.”
The book was about an actress who has an affair with a married man, although she was adamant it wasn’t based on her own life.
The early stages of her romance with David appear to have been as traumatic as her star-crossed affair with Smithy in Gavin and Stacey.
Ruth also admitted how much she has enjoyed being a stepmother to David’s three children.
She once declared that she’d experienced “all the joy of motherhood without the pain of childbirth”.
Since making it big, Ruth revealed she rarely appears on the celebrity circuit, often saying she feels more at home jogging in Cardiff’s park and shopping in her local Tesco.
Do you have a story to sell? Get in touch with us at email@example.com or call us direct 0207 29 33033