Until the last year or two of their marriage, my parents kept most of their arguments out of sight of the kids. Out of sight, but not out of sound. "They're at it again," my brother would whisper from the bed next to mine as the shouting raged downstairs. By the time I was about 14, hostilities were more overt on both sides. Mealtimes became wars, the dinner table was a battlefield, the television a weapon, the kids innocent bystanders taken hostage.

The worst fight, the mother of all wars, occurred around the dinner table, its main weapons: a plate of spaghetti bolognaise and a major revelation about my older brother, Alan [not his real name].

I guess my mum felt powerless. She saw her marriage crumbling and determined to use any weapon she could, however desperate. "Why don't you tell Alan why you never show him any affection?" she screamed at my dad. "I show him just as much affection as the others. And he doesn't need to know that." "It's time he knew. Alan, the reason your dad favours the others is that he's not your dad."

They told us that in the early sixties, when my dad had been stationed at an airforce base in Hampshire, my mum had had an affair with another man, and had become pregnant. Alan wasn't my dad's son. He was only my half-brother.

We didn't get to hear much more of this, because my dad said something about my mum and she retaliated by pushing her plate of spaghetti into his face. He sat there, continuing to eat, bits of spag bol dripping off his moustache.

My brother quietly got up and left. I followed shortly after, and found him brooding in a bus shelter.

We've rarely spoken about it since, and I'd pushed it to the back of my mind.

But when I started working at this company, I was in a meeting with a guy who was the spitting image of Alan. He could have been his brother, or half-brother at least. He certainly looks a lot more like my brother than I do. But I rationalised that it was just a coincidence - lots of people look alike, it doesn't mean they're related. But at a meeting last week, he said he was from Hampshire. From the very town my dad had been stationed in, the town my brother was born in.

It still is most likely a coincidence. And what could I possibly say to him? "Hey, did your dad ever have an affair?"

I suppose I could tell my brother - my mum may have told him the surname of his father. That's if I knew how to get hold of my brother - he retreated from the family after he left home. I haven't heard from his in three years, the last email I sent him was bounced back.

But why stir things up? Better to leave things as they are. It probably isn't the same guy, so no point getting his hopes up only to have them dashed. And if somehow he is the same guy, well, perhaps he wasn't married at the time, and has never told his wife and kids about his secret love-child.

So I'll say nothing, and just be struck by the resemblance every time he walks past my desk. At least I get to see my brother occasionally.