Ronald Reagan beside his wife Nancy Reagan during his inaugural ceremony in Washington. File/AFP

Patti Davis, the daughter of late President Ronald Reagan and First Lady Nancy Reagan, has written in a new memoir that her father only married her mother because she was pregnant.

Davis, 71, writes in Dear Mom and Dad: A Letter About Family, Memory, and the America We Once Knew that ahead of his divorce from actress Jane Wyman, he had “made a pact” with her not to remarry before her.

Davis adds that Reagan “was not exactly anxious to get married again”.

“Travelling back, you realise that the whole story of your family is bigger, messier, and often more tender than you once believed,” the daughter, who was born six months after her parents were married in 1952, writes.

Wyman and Reagan had three children during their nine-year marriage, one of whom died shortly after birth.

During a dinner at the Hollywood restaurant Chasen’s, Nancy revealed to the future president that she was two months pregnant, Davis writes, according to the Daily Mail.

The daughter writes that her father quickly left the table to phone Wyman to tell her he had to break the pact to marry Nancy before the birth of their child.

They married on 4 March 1952 and Davis was born six months later, on 4 October of that year. Reagan officially divorced Wyman in June 1949.

Kitty Kelley poses for a photograph. File AP

Kitty Kelley, Nancy’s biographer, has stated that Reagan dated actress Christine Larson for a year following his second marriage, saying that he had been “tricked” into the union.

Kelley has also claimed that Reagan was with Larson during the birth of Davis and that Nancy had an affair with Frank Sinatra while she was first lady.

The 186-page book is written in the form of a letter to her parents. Davis writes that her birth was a flaw in her mother’s “romantic illusion” with the president.

Davis outlines her difficult relationship with her mother, but she would still go on to change her last name to Nancy’s maiden name – Davis.

Patti Davis writes that she often got high and at times thought about taking her life, describing home life under Nancy’s stern rule as “stiff and strict”. Meanwhile, Reagan is described as a doting father, teaching her to ride horses, fly kites, and have theological discussions about “the blue waters of heaven”.

The daughter writes that she often got high and at times thought about taking her life, describing home life under Nancy’s stern rule as “stiff and strict”. Meanwhile, Reagan is described as a doting father, teaching her to ride horses, fly kites, and have theological discussions about “the blue waters of heaven”.

“I never stood a chance with you. The intractable war between you and me, Mom, kept brewing often to a boil – it was a dark tide moving beneath us,” she writes to her mother, describing her as cold with a tendency to fly into “formidable” fits of rage.

“I don’t remember ever walking into our home with a sense of security and a feeling I belonged,” Davis notes.

She adds that her father’s rightwing politics later created a rift between them, writing, “I had more truthful and raw conversations with Lincoln’s ghost than I was able to have with you,” in reference to her stays in the Lincoln bedroom in the White House.

Reagan died in 2004 at the age of 93 after a long fight with Alzheimer’s. Nancy passed away from heart failure in 2016. they’re both buried at the Ronald Reagan Presidential Library in Simi Valley, California.

The Independent