Not being a fan of reading labels before drinking, I saw the word "triple" and

Closer attention to the label reveals that this is "triple fermented", which is one explanation given for the origin of the tripel name, but not the usual one. Anyway, this is no tripel. It's a much smoother, sweeter golden ale, more along the lines of Duvel or Piraat to my mind.
The dominant flavour is fruit. I was getting the sharpness of pears while Mrs Beer Nut detected bananas. This, of course, is our old friend 3-methyl-1-butyl acetate, generally known as isoamyl acetate to its friends. I had never associated it with pear flavours before, but Wikipedia tells me that pear essence is another name for this ester. Mrs Beer Nut has a degree in organic chemistry, but we don't talk about esters much for some reason.
The chemistry aside, this is a highly enjoyable beer: flavoursome, complex, yet easy going. 75cl doesn't last nearly long enough. The full-yet-effortless drinkability is something rarely found at 9% ABV, even in Belgium.
Of the three Unibroues, dark Trois Pistoles is the one I'll be running back to first. But I'd be happy with any of these whatever the season.