Some romance tropes just hit right—and the best friend’s brother or best friend’s sister trope is one of those enduring favourites. Equal parts thrilling, forbidden, and deeply emotional, it’s a setup that never seems to lose its charm.
What’s the Appeal?
The best friend’s sibling trope taps into something profoundly human: the thrill of wanting what feels just out of reach, and the fear of losing what matters most if you reach for it anyway.
At its heart, this popular romance trope is driven by the tension between intimacy and inhibition. The characters often share a long history, which makes their connection feel grounded and believable—but that same familiarity is exactly what makes the attraction feel dangerous. It’s the forbidden layered over the familiar. You’re not falling for a stranger; you’re falling for someone you’ve seen across dinner tables and family holidays, someone woven into the fabric of your life.
But there’s a deeper reason why this trope hits so hard—it skirts the edge of a deeply troubling taboo: incest.
Incestuous relationships in novels are weirdly popular when done well. Think Cersei and Jaime Lannister in Game of Thrones, or Chris and Cathy in Flowers in the Attic. The problem with the incest trope is that it’s too gross for most people to openly enjoy. We don’t love Cersei and Jaime as people, or root for them as a couple, but we’re utterly fascinated by the carnage their forbidden love causes.
The best friend’s brother or sister trope allows us to fully immerse ourselves in an almost incestuous romance without that nasty ick feeling that comes with the couple actually being related. It gives us all the closeness, all the taboo tension, and all the risk of betrayal—without crossing a line that would make most readers uncomfortable.
It’s transgressive, but just safe enough.
And when done well, the best friend’s sibling trope isn’t just about the thrill of secrecy. It becomes a story about choosing someone even when you shouldn’t—when loyalty, friendship, and common sense all say no, but your heart says otherwise. That emotional gamble, the possibility of losing something real to gain something irresistible, is what makes this trope so compelling.
There’s always something at stake—a friendship, a sibling bond, a sense of safety—and that risk makes every touch, every look, every “No, we shouldn’t!” moment hit harder. The best stories in this category understand that the tension isn’t just will they or won’t they?—it’s should they?
And when they finally do, it’s not just about physical attraction. It’s about choosing each other with full knowledge of the consequences. That kind of love—risky, reckless, but deeply felt—is what makes the best friend’s sibling trope so enduring.
What Makes It Work
The best friend’s sibling trope has remained a reader favourite for good reason. It blends emotional depth, built-in tension, and the thrill of crossing a line you were never supposed to even look at. But what exactly gives this trope its staying power?
Forbidden But Familiar
The characters already know each other—often from childhood or adolescence—which means there’s emotional history baked in. They’ve seen each other at their worst (awkward phases and all), but something’s shifted. Suddenly, the goofy kid brother is six-foot-something and devastatingly charming. Or the once-annoying older sister is now confident, magnetic, and impossible to ignore.
Risk And Reward
Going after your best friend’s sibling risks more than just rejection—it could blow up one of the most important relationships in your life. That emotional gamble raises the stakes, which makes the romance feel high-risk and high-reward.
Built-In Proximity
Sleepovers, holidays, family dinners—this trope thrives on proximity. And when you’re suddenly hyper-aware of someone you’ve always seen as off-limits, that closeness becomes electric. If you’re a fan of the forced proximity trope, you’re likely to enjoy this one too. It’s not quite the same, but there’s a similar energy as hanging out with your bestie comes with a bonus sibling you can’t quite get away from.
Emotional Evolution
This trope often involves characters re-evaluating everything they thought they knew about each other. It’s about growth, forgiveness, and falling in love with someone real—not the idea you had of them as a kid.
Common Variations
The best friend’s sibling trope is endlessly adaptable. Whether the story leans toward comedy, angst, or steam, these familiar twists keep things fresh while delivering all the emotional impact readers crave. Here are a few of the most popular variations:
The Protective Brother
This version usually centres on a female protagonist falling for her best friend’s older brother—someone she’s known forever, who now seems… different. The catch? He’s fiercely protective, often to a fault. Expect tension, over-the-top reactions, and some deeply satisfying moments when he finally lets his guard down. This setup often walks the line between heartfelt and hilarious.
The ‘Don’t Tell’ Sister
Flip the script, and you’ve got a main character quietly falling for their best friend’s sister—either younger or older. Maybe it’s a forbidden hookup that turns into something more, or a lifelong crush they’ve never dared admit. The secrecy here turns up the heat, especially when family dynamics make every glance or touch feel dangerous.
The One Who Grew Up
Sometimes it’s not the older sibling, but the one who was always considered ‘too young’ or ‘just a kid’. This version leans into the glow-up fantasy: the protagonist suddenly sees the best friend’s younger sibling in a completely new light—and can’t look away. It’s a great recipe for surprise attraction, awkward realisations, and that delicious moment of wait… when did you get hot?
Speaking as a girl who grew up crushing hard on more than one of her brother’s (much older) friends, I can say from personal experience how hot it is to suddenly have one turn round, look at you, and see you as a woman.
And a woman they find suddenly sexy!
Popular Best Friend’s Brother/Sister Novels
If you’re craving all the tension, secrecy, and emotional payoff this trope has to offer, here are some standout reads that deliver it in all its irresistible glory:
Romancing Mister Bridgerton by Julia Quinn
In this fourth installment of the Bridgerton series, Penelope Featherington has harbored a secret affection for her best friend’s brother, Colin Bridgerton, for years. As Colin returns from his travels, he begins to see Penelope in a new light, leading to a romance filled with wit, secrets, and self-discovery.
Lost and Lassoed by Lyla Sage
Gus Ryder, a dedicated single father and rancher, is overwhelmed with responsibilities. When his sister’s best friend offers to help care for his daughter, Gus is hesitant due to their contentious history. However, as they spend more time together, their mutual disdain transforms into unexpected affection.
Twisted Hate by Ana Huang
In this third installment of the Twisted series, Jules Ambrose and Josh Chen have always been at odds. Jules, a spirited redhead, and Josh, a cocky aspiring doctor, share a mutual animosity that masks an undeniable attraction. As they navigate their fiery dynamic, past demons resurface, challenging their budding relationship.
The Right Move by Liz Tomforde
Indy Ivers finds herself in need of a place to stay, leading her to move in with her best friend’s brother, NBA star Ryan Shay. To improve his public image, Ryan proposes a fake dating arrangement with Indy. As they cohabit and present a united front, their pretend relationship begins to blur into something genuine.
Rewrite Our Story by Kat Singleton
Mare, an aspiring writer, returns to her hometown of Sutten Mountain and crosses paths with her childhood crush and best friend’s brother, Cade. Old feelings resurface as they confront their shared past and the possibility of a future together. This second-chance romance delves into themes of love, loss, and redemption.
From Lukov with Love by Mariana Zapata
Figure skater Jasmine Santos has faced numerous setbacks in her career. An opportunity arises when she’s offered a partnership with Ivan Lukov, her best friend’s brother and a renowned skater. Despite their history of mutual annoyance, their partnership on the ice leads to a deeper connection off it.
Cruel Winter With You by Ali Hazelwood
Two former childhood friends are reunited during a blustery winter storm, rekindling old memories and igniting new feelings. As they navigate their shared past and the challenges of the present, they must decide if their bond can withstand the test of time.
Homerun Proposal by Maren Moore
In a twist of fate, a woman’s proposal to lose her virginity is mistakenly received by her best friend’s older brother, Lane Collins, the university’s star baseball captain. This unexpected turn leads to a complex mix of emotions and a reevaluation of long-held feelings.
Darling Venom by Parker S. Huntington
Charlotte and Kellan form an unlikely bond after a chance rooftop encounter. Years later, Charlotte becomes entangled with Tate, Kellan’s older brother, leading to a tumultuous relationship filled with passion, grief, and healing.
Stay With Me by Brooke Montgomery
After a text message about a secret crush is misinterpreted, a woman finds herself confronting her feelings for her best friend’s brother, a tall, dark-haired cowboy. Their close quarters and shared history make for a compelling tale of love and self-discovery.
Small Town Swoon by Melanie Harlow
Ari has always harboured feelings for her best friend’s older brother, Dashiel Buckley (bonus points for use of the name Dashiel!). When he returns to Cherry Tree Harbor for a wedding, Ari is determined to keep her emotions in check, but old attractions prove hard to resist.
Change on the Fly by Maren Moore
Holland has secretly loved her best friend’s brother, Reed Davidson, a professional hockey player. When Reed gains custody of his nephew, Holland steps in to help, leading to unexpected closeness and the possibility of something more.
Truly Madly Deeply by L.J. Shen
Calla Litvin returns to her hometown to support her mother and rekindles her friendship with her former BFF, Dylan. However, Dylan is closely associated with Calla’s longtime crush—her best friend’s brother—leading to a complex web of emotions.
This Summer Will Be Different by Carley Fortune
During a vacation on Prince Edward Island, Lucy becomes involved with Felix, unaware that he is her best friend’s younger brother. Their undeniable chemistry challenges their resolve to keep things casual.
These novels offer diverse takes on the best friend’s sibling trope, each weaving unique narratives that explore the complexities of forbidden attraction, familial bonds, and the pursuit of love.
Why Best Friend’s Brothers And Sisters Are Here to Stay
Romance readers love emotional stakes, and this trope delivers. It’s a potent mix of yearning, risk, and inevitable fallout—and when done right, it pays off with some of the most satisfying slow burns or emotional confessions on the page.
Whether you’re in it for the angst, the giddy secrecy, or the delicious moment the best friend finds out, the best friend’s sibling trope will always have a well-earned place in romance fiction.
