The Swansea-born businessman – who gave financial advice to the Royals, including the Queen – had another wife and children, who were, in turn, completely unaware of Minnie, her elder sister Kate or Gaynor.
Consequently, the star knew very little of her father's side of the family. But becoming a mother to four-year-old Henry piqued her interest. Minnie recently decided to take part in the BBC One genealogy show, Who Do You Think You Are? in an attempt to discover more about her father.
She was astounded to find out that Ronnie was a World War hero, who was awarded a medal for bravery.
During filming for the show, Minnie discovered that her father was a member of the RAF during the Second World War and that he won a medal for his part in the battle of Heligoland Bight in 1939. Reading about his heroics with tears in her eyes, she found out that he put out a fire with his hands in a desperate bid to save his plane and his crew during a daring raid on a German airbase.
When the plane crash-landed in the freezing waters of the North Sea, Ronnie then managed to launch a dinghy, helping to save the lives of three injured crew members, earning him the Distinguished Flying Medal.
But, Minnie discovers, he poignantly threw it into the Thames because he didn't think he deserved it after failing to save his best friend Walter Lily. He went on to have psychiatric treatment as he struggled to come to terms with the event.
"It seems unbelievable what he did. It reads like a movie script," Minnie said of her discovery. "I feel very close to a part of my father that I never knew."
Speaking about her decision to take part in the show, Minnie added, "Having a baby obviously changes everything and Henry made me want to connect with who I really am I suppose.
"My dad died a year and three months after Henry was born and I'm so grateful that they had even a little amount of time together, and Dad just delighted in Henry.
"My parents met in 1962, and they were together for 13 years. They broke up when I was six, and during that entire time he was married to someone else and had another family. I didn't know until I was about 12. My dad lived a very split life. We just did not talk about where he came from.
"He spoke very succinctly about his mum and his dad, and I never met my grandparents or even saw a photograph of them together, and I always wondered what they looked like.
"I want Henry to have a different experience to what I had. Where I come from there are these big gaps, and I would like to fill those gaps for him."
Who Do You Think You Are? airs on BBC One on Wednesday at 9pm