AMERICA’s sweetheart Doris Day has been hiding a crushing heartbreak – and a strange secret – from her devoted fans, an ex-employee reveals!

Day’s former “dog chef” Diana Barron Nave exposes the torment and unusual life of the reclusive 89-year-old Hollywood legend who lives in a fabulous Carmel, Calif., mansion.

Nave, 58, who worked for the beloved star in 2000 and 2001, claims Doris: Keeps an expensively decorated “baby nursery,” complete with a crib, that is out of bounds to everyone but herself – and she spends hours there rocking a baby doll as a means of “coping.”

Doris is still plagued by grief over the death of her only child, son Terry Melcher, and wishes she’d spent more time being a mother and less chasing her movie star dreams.

 “Doris never really got to be a mother, and she’s not really been a grandmother – and those things really bothered her,” says Nave, who became intimately acquainted with the star. After answering a newspaper ad seeking a “dog chef” in late 2000, Nave says she was hired for $10 an hour and spent five afternoons and evenings a week preparing food and feeding the “Calamity Jane” star’s rescued dogs and cats.

Day dotes on her menagerie, the former staffer says.

“I even cooked fresh chicken and prepared meat loaves – Doris feeds her animals nothing but the best,” Nave says.

While the way Doris pampered her pets was remarkable, Nave was taken aback even more when she discovered a room, decorated like a nursery, that was home to an eerily lifelike baby doll.

Attached to Doris’ own bedroom, the space was strictly off-limits and the star “must have spent $10,000 to $15,000 decorating that room,” says Nave, who passed a polygraph test.

Nave said she was shocked one day when she entered Doris’ bedroom to tend to some animal business and looked into the “nursery” to see her boss sitting in a rocking chair, holding the baby doll in her arms.

“Some days she spent hours in the nursery,” Nave says. “It seemed that she desperately wanted to be a mother – and sitting with the doll was her coping mechanism for dealing with her feelings,” Nave claims.

“She would even order new clothes for it. I could see her through the glass panes in the room’s French door. But I was warned by the estate manager never to go in there!

“I just gathered that this rocking the ‘baby’ was how she coped with her feelings of regret,loss and, probably, loneliness.”

Dr. Lillian Glass, a top Beverly Hills behavioral expert, who has not treated Doris,  says “many women use dolls” to help fnd peace in a troubled world. “They bring back a woman’s maternal instinct and take them back to a time when they were very happy,” the expert explains.

 “Doris lost her only child, and for her the doll is probably a huge comfort. She’s into comforting and nurturing – just look at the great work she’s done for animals – and the baby doll likely lets her express that in another way.

“And the doll might return her to a time in her life when she was her happiest – when she was a new mother with a baby to care for.”