It happened to me a few days ago when this photo was posted. I'd not seen it before.
The picture was taken in Macosquin on 12 July 1965 and the man on the left is my dad, Barry Snr, aged 29.
Here he is close up.
I showed the photo to Jamie and Charlotte earlier tonight and asked if they knew who it was.
Without taking a breath, Jamie said: "Is it the Duke of Edinburgh?"
So, so close.