Four new illustrations by beloved children’s author Beatrix Potter have been discovered by staff a National Trust property in the UK.

The line drawings were found hidden inside books at Melford Hall in Suffolk. “Whilst we were going through some of the books we discovered a drawing tucked inside, it was classic Potter style and we immediately knew it was one of hers,” said house manager Josephine Waters of the discovery, which occurred during planned conservation work, in a statement.

One of the newly-discovered Beatrix Potter drawings. Courtesy of the National Trust.

She called the find “an absolutely spine-tingling moment,” saying “I remember all the hairs on the back on my neck stood up as we realized what we’d found.”

The Peter Rabbit creator, whose 150th birthday will be celebrated July 28, was a regular visitor to the estate. It was the home of her cousin, Ethel Leech, who was married to William Hyde Parker, between 1899 and 1916. Today, Melford Hall still owns one of the original prototypes for the stuffed toy version of Jemima Puddle-Duck, one Potter’s best-loved characters, which the author gave as a present to the Hyde Parkers.

The original toy Jemima Puddleduck. Courtesy of Melford Hall.

“When we were children we just loved it when she [Beatrix] arrived, for she always brought a cage with mice, another with a hamster or a porcupine and a third with something else in it,” Ethel’s son, William Hyde Parker, once said, as quoted on the Melford Hall website. “It was such fun for all us children.”

Despite Potter’s previous ties to the property, no one suspected that she had left her artwork behind. In light of the discovery, Melford Hall, which is still home to the Hyde Parker family today, will host an exhibition of the long-lost work.

One of the newly-discovered Beatrix Potter drawings is of the fireplace at Melford Hall. Courtesy of the National Trust.

“We do not know the exact dates for all the drawings,” said Waters, “but they give us a glimpse into the world of Beatrix beyond the children’s stories and help us to imagine more about who she was as a person, and particularly who she was when she was on holiday and drawing for her own entertainment.”

It isn’t the first time an important drawing has turned up at a historic site in recent years. A long-lost study for Frederic Leighton‘s Flaming June was found hanging on the back of a door in a Surrey mansion last year. Meanwhile, at Germany’s Karlsruhe State Museum, an intern discovered a large cache of Giovanni Battista Piranesi drawings misattributed to architect Friedrich Weinbrenner.

Two of the newly-discovered Beatrix Potter drawings. Courtesy of the National Trust.

“Beatrix Potter’s Melford: Holiday Sketches 1899–1916” will be on view from July 13–October 30, 2016.