When my sister and I were young girls, we pretended to be twins. Born only one year apart, for a time Darya and I were roughly the same height and had the same chestnut hair and hazel eyes. Eventually, despite being younger I grew a little taller, while Darya’s face became angular, its delightfully moody planes often punctuated by a smile that is joyful and mischievous. Later still, she began colouring her hair till it was fiery and dazzling, painted like October leaves in Quebec’s Gatineau Park near where we lived.

As for me, my face has remained broad, almost Slavic through the cheekbones, tapering to a small chin and perched on a long neck. I’m told I look reserved and haughty, which is sometimes useful.

When we were twins, Darya and I would meticulously pair our clothes, rummaging through cupboards in search of shoes that seemed to match, frustrated by any small compromise. Our father once returned from a business trip with matching blue velvet skirts for all four of us girls, undoubtedly oblivious to how this well-intentioned but unimaginative gift would fuel the fantasy Darya and I shared. Forget the random coincidence of merely similar white turtlenecks or red wool tights, we thought. Our skirts were identical and so – fingers crossed – were we.

Our apparent sameness was often rewarded with admiring smiles from passers-by. ‘How pretty!’ they would coo. ‘Are you girls twins?’ Despite our intention to deceive we didn’t have the courage to lie outright so instead we would beam back at them silently, our blushing smiles calibrated to convey agreement without committing us to a blatant fib.

Eventually we outgrew our obsession with twins, but I have often wondered about this common childhood fascination. Is it merely fancy dress, pretending to be something you aren’t and – better still – hoodwinking naive grown-ups? Or perhaps we were intrigued by the trompe l’oeil of being identical in the most minute detail, yet utterly discrete at the same time?

Years ago, I read about the famed Minnesota Twins Study, which showed that even twins separated at birth unwittingly found ways to be identical. Many of them had never laid eyes on each other, yet they had similar jobs and the same number of children and sometimes their spouses bore the same names.

Of course, twins examined this way help us explore the nature/nurture question, providing the closest available approximation of two paths offered to (almost) the same person. But for me, this study poignantly exposed the relentless pull of an unbreakable connection, and I suspect this is what Darya and I longed for. Since she was diagnosed with breast cancer five years ago I have often wished to be Darya’s childhood twin again, to believe that her pain and fear could be mine and that she could have some relief from them. But I know that we are not twins; we are separate people wearing clothes we choose for ourselves. Now I am merely Darya’s sister who holds her hand and loves her fiercely.