UPDATE: August 24, 2020: An earlier version of this article contained an unauthenticated photograph of Lewis Carroll and Alice Liddell. 

This year marks the 150th anniversary of Lewis Carroll’s masterpiece, the wildly imaginative book Alice’s Adventures in Wonderland (1865). But the recent discovery of a shocking image within his photograph collection has upstaged the celebrations, suggesting that the English author’s interest in children might not have been so innocent after all.

Tomorrow, BBC will broadcast a controversial new documentary entitled The Secret World of Lewis Carroll, in which it will be revealed that Carroll—a photographer as well as a fiction writer and mathematician—took countless pictures of young girls in his lifetime. In most of the images, the children are dressed, but there are others in which they are naked.

Carroll—whose real name was Charles Lutwidge Dodgson—set up a photography studio in his rooms at Oxford, where he was a mathematics lecturer. There, he took self-portraits and portraits of famous artists of the era like Dante Gabriel Rossetti. But photographs of children dominate his production, and amongst the most troublesome pictures, there’s one that unnerved the BBC experts particularly.

Lorina Liddell

It is an image of a pubescent girl called Lorina Liddell in the nude in a full-frontal pose, described in the documentary as an image that “no parent would ever have consented to,” the Telegraph reports. The controversial photograph was found in a French museum, with a note on the frame attributing it Carroll.

Lorina was the elder sister of Alice Liddell, the little girl who inspired the famous Alice character. Carroll befriended the Liddell family, and became infatuated with the couple’s daughters: Lorina, Edith, and, especially, Alice. In the BBC documentary, the literature Professor Hugh Haughton says that Carroll’s relationship with the Liddell girls was known to have a “huge intensity” which would seem “pretty strange now.”

“My understanding is that he was in love with Alice, but he was so repressed that he never would have transgressed any boundaries,” says Vanessa Tait, great-granddaughter of Alice Liddell, in the documentary. She adds that the explicit photograph may explain the rift that made Carroll break contact with the Liddell girls in 1863, when Alice was 11 years old. Crucially, Carroll’s diaries from April 1858 to May 1862, a period which coincides with his friendship with the Liddell girls, are missing.

Speaking in the documentary, the acclaimed writer Will Self doesn’t mince words: “I think, [Carroll] was a heavily repressed pedophile, without doubt. It’s a problem, isn’t it, when somebody writes a great book but they’re not a great person.”

But not everyone agrees with Self. A new biography, Lewis Carroll, The Man and His Circle by Edward Wakeling (2015), presents Carroll as a respectable member of society, with friends in high places. Yet, as Elizabeth Winkle writing for the New Republic ponders: “Is it possible that history has misread his collection of photographs and his relationship with Alice? Yes. Is it possible that he was amiable but also a pedophile? Yes.”

Although the details about Carroll’s relationship with children in general, and with the Liddell girls in particular, might never be known, the evidence that he had a somewhat unhealthy obsession with minors seems overwhelming. “It’s sad that that’s the thing everyone is going to want to know, especially in the year of the anniversary of the book,” says Tait in the documentary.