As a woman who is unafraid to rewear the same outfit on high-profile occasions, the Princess of Wales is well-known and much-admired for her thriftiness.

But at the Trooping of the Colour on Saturday, she eschewed rewearing one of her previous looks in favour of rewearing someone else's.

Not literally, of course, but while her pale blue Catherine Walker 'Lafayette' coat dress hadn't been worn before by Catherine, eagle-eyed royal watchers may nonetheless have noticed that it looked rather familiar. 

In colour and style, it bore a striking resemblance to an outfit worn by her late mother-in-law, Diana, Princess of Wales. 

During the 1980s, Diana wore a coat dress in a near-identical hue, with the same white trim, by the same designer, on a number of prominent occasions, most notably at Prince William's first Easter service, held at St George's Chapel in Windsor Castle in 1987.

Very sweetly, a then-four-year-old Prince William was dressed in a similar but scaled-down version of his mother's Catherine Walker coat, in the same delicate shade of pale blue, with the same double-breasted buttons and patch pockets. 

Perhaps sensibly given his spirited nature, Catherine stopped short of dressing her youngest son, Prince Louis, 8, in a miniature version of her own coat. 

Instead, the young prince wore a smart double-breasted navy blue suit, his pale blue tie the only extent to which he twinned with his mother. Prince George, 12, also wore a navy suit and pale blue tie.

Princess Charlotte, 11, also elected not to twin, instead coordinating with the style and white accent colour of her mother's coat dress in a bespoke white dress by Alessandra Rich featuring puff sleeves, double breasted buttons and a Peter Pan collar. 

She teamed her dress with white 'Nicole' ballet flats by Pretty Ballerinas, £179, and wore her hair loose and swept back from her face by fastening it with a £295 satin bow 'Fauna' clip by Jane Taylor Millinery.

Also in white was the Duchess of Edinburgh, whose cady Roland Mouret midi dress was similar in style and colour to Princess Charlotte's. 

She teamed it with a diamond brooch and white straw and feather hat, also by Jane Taylor Millinery.

Catherine completed her look with white '105' pumps by Gianvito Rossi, £710, pearl 'Cavolfiore' earrings by Cassandra Goad, £7245, and a wide-brimmed saucer hat by milliner Philip Treacy whose pale blue and white hues perfectly complimented her coat dress. 

Pinned to her lapel was the Irish Guards regimental brooch, paying tribute to her military role.

With Ascot starting next week, any guests still undecided about whether to buy a wide-brimmed hat or a fascinator will no doubt be swayed by Catherine's decision to supersize her hat. 

Like Diana before her, where the princess leads, other women tend to follow. When it comes to millinery, few would bet against Ascot being full to the brim.