Katharine Hepburn's (search) estate is expected to be worth untold millions because, as well as being born rich, she lived an incredibly frugal lifestyle and hoarded closets full of priceless movie memorabilia at her Connecticut home.

"She may have millions more than even her accountants are aware of -- because she saved so many things from her movie career," a friend of the late actress told The Post last night.

"And she was a real homebody. She always preferred a home-cooked meal to a fancy restaurant or a night out on the town."

Although no official details of the actress's bank accounts and possessions have been released, another friend estimated her estate could be worth "$40 to $50 million conservatively."

"She may be worth a mint after it's all sorted," the pal said. "Looking at her property alone, the East Side townhouse she sold a while back was worth around $10 million and her Saybrook [Conn.] place is a $10 million to $12 million property."

And Hepburn's real-estate holdings only scratch the surface of her worth.

It helped that she was born with a silver spoon in her mouth -- the daughter of Katharine Houghton Hepburn, a member of the rich, socially prominent family that founded the Corning Glass Works, and Dr. Thomas Hepburn, a prominent surgeon.

And she was a pack-rat. Over the years, the grand dame of Hollywood kept many of her costumes and props from movies such as The African Queen (search) and Adam's Rib as well as her four Oscars and numerous other awards - all of which are now worth millions.

In her day-to-day life, friends say, she was much happier fixing a cup of tea and a plate of biscuits for a friend at home than lunching at The Plaza.

"She was very frugal. She didn't spend her money on clothes, she wouldn't eat out and while she had a chauffeur, the car was a beat-up old station wagon," said her friend, Stephen Silverman, an author and former Post reporter.

Silverman said when Hepburn wrote the intro to his 1989 bio of director David Lean, "she was given a few thousand dollars for it. She just looked at the check and I thought maybe it wasn't enough. Then she said to me, 'Here, you take it.'"

Hepburn's estate is expected to rise even higher when a secret biography cum memoir on which she worked for years -- but demanded not be published until after her death -- hits bookstores July 11.

G.P. Putnam (search) will put out a 500,000-copy first printing of Kate Remembered, written with author A. Scott Berg.

Berg said the book will be part reminisce and part reflection, collected from conversations Berg had with the actress during the 20 years he worked with her on the project.

"Almost from the moment I met Katharine Hepburn more than 20 years ago, she began revealing stories of her life, not just professional anecdotes, but personal stories," said Berg.

"In the last few weeks of Hepburn's life, I wrote the final paragraphs, the hardest I've ever had to write," Berg said.