'He has only his selfie to blame'— a woman realised her boyfriend of four years was cheating after spotting a tiny detail in his selfie photo.

Sydney Kinsch shared a TikTok video of how she made the bombshell discovery that her partner was cheating on her.

And her jaw-dropping video racked up a whopping 1.4 million views in less than 24 hours.

The viral video shows Sydney superimposed over her now ex-boyfriend's selfie wearing a pair of sunglasses.

At first glance, it's hard to spot what is unusual about the photo.

But when Sydney eventually moves to the left, she reveals her boyfriend's sunglasses' reflection.

The reflection shows what appears to be a blonde-headed woman's legs poking out the window on the passenger's side.

Sydney had captioned the video:

"Check the reflection in your boyfriend's sunnies, ladies."

The video has garnered more than 208,000 likes and shocked TikTokers flooded with thousands of comments. And lots of people were impressed with her detective skills.

One curious woman asked:

"Ok, but what did you respond? I need to know."

And Sydney replied:

"I called him and asked if he realized he sent me a b**** in his Snapchat, but he had no idea."

"So I sent it to him, and he called me crazy. He then said it was our friend's gf and that's he's allowed to have friends."

"He was with 'like 5 people....I found out a week later ALL the details."

In another comment, she explained that her boyfriend had been cheating for a month.

One woman responded:

"What [people do] in the dark comes out in the reflection of your sunglasses, always."

While another said:

"Guys always thinking they can pull a fast one on us."

Others revealed that Sydney's experience was far from an outlier. Many admitted they too had busted cheating lovers via reflective photos.

One shared:

"This legit happened to me."

"My ex took a selfie to send me, and I saw the chic in his glasses reflection lol."

"He was at a restaurant."

Another said:

"How I caught my ex too. Reflection in a window."

A third replied:

"Lmao, I recognized his tattoos in the mirror in a girl's story."

This jaw-dropping revelation isn't the first time a photo has played a pivotal role in a dramatic tale of infidelity.

Earlier this year, one furious ex-wife got public revenge on her cheating husband by posting flyers of their family photo around his new town.

The flyers had a photo of a happy family posing together, with a message beneath it.

It read:

"Abandoned his wife and kids in New York to come to [the town] to sc** MILFs."

"Some neighbors you have!"

"He's still married and living with another woman."