It was so utterly unexpected. I’m sitting in the viewing gallery, next to his mother from whom I am estranged, and Dylan is walking along the poolside, in a line, among the children against whom he will compete. Voices echo and my nostrils are aware of chlorine.

He’s nine or ten, wearing a swimming cap, bright red in the face, head bowed, staring at the non-slip floor. Self-conscious – a trait we share too readily – and no doubt fearful. It’s his first competitive feat in front of the viewing public. He’s representing Highams Park School at the backstroke.

And it hits me, out of the blue. I choke. My throat blocks off its airways and my skull tightens, begins to pulsate. Suddenly I’m locked inside my only head and this tsunami of emotion wells up. My vision blurs. I’m gazing at my son through a watery lens that deepens and wobbles at my lower eyelids.

I tense, try to hold back the tears – how daft, a grown man crying at a swimming gala! – but their gathering weight overwhelms the surface tension and they tumble down my cheeks like children down a grassy knoll in the summertime.

I sit there, stock still, in shock, locked inside this emotion – pride – wondering whether anyone has noticed.

Surreptitiously I raise a cuff to each cheek and wipe away the guilty traces. Daft, really.

Dylan doesn’t win the race. The result is immaterial.

There are plenty of emotions, though few so powerful that they can reduce one to salt-wash as an adult. Pride in ourselves cannot do it – unless that’s what overwhelms an Olympic athlete up on the medals podium; I’m yet to experience that – only pride in our children.

Of course I am proud of both my kids, on a daily basis, but to compel actual tears is a bewildering extreme.

It has happened two or three times during all my 16 years of fatherhood. That swimming gala sticks in my mind because it was the first time and I had no clue that such intensity was possible.

Partly, I suspect, I reflected my own childhood in him at that moment poolside: I’d been forced into swimming galas while my parents spectated from above; Speedo trunks on and a fear of failure. Perhaps it reinforced that father/son generational cycle, of learning and graduation. Perhaps also I sensed my own distant, departed childhood and mourned its loss.

Whatever it was, I was staggered and immensely grateful that it happened. Parenthood has its many travails, but to be moved to tears through pride in another is some gift.