The princess's dress and hat had been worn together before
Princess Anne has worn the same dress she wore to the wedding of Prince Charles and Lady Diana Spencer 27 years ago to another royal wedding.
The Princess Royal wore the white dress with yellow floral print to Saturday's wedding of Lady Rose Windsor and George Gilman, at the Queen's Chapel, London.
The 57-year-old even completed the outfit with the same hat she wore to Charles and Diana's wedding in 1981.
Kate Middleton also attended, but without boyfriend Prince William.
Lady Rose, 28, is the youngest child of the Duke of Gloucester, who is a relation of the Queen.
She observed the tradition of the bride wearing something old with a tiara that belonged to Queen Mary.
Her dress was designed by Franka Couture.
Her bridesmaids were Mr Gilman's nieces, Lily, three, and Alice, nine, and her pageboy was five-year-old Jesse Grylls, son of the TV star Bear Grylls.
Other guests to attend included Princess Anne's son Peter Phillips and his wife Autumn.
Princess Anne has famously recycled a number of items of her wardrobe in the past.
The yellow hat she wore to her daughter Zara's christening in 1981 reappeared on a trip to Khartoum in 1985 and again at Ascot three years later.
Similarly, a midnight blue dress was dug out in 1999 - 23 years after its first outing at a function in Berlin in 1976.
When asked about her frugality, Princess Anne has said: "A good suit goes on for ever. If it is properly made and has a classic look you can go on wearing it ad infinitum.
"The economy is bred into me. My parents believe that things are not to be wasted."
Hilary Alexander, fashion editor at the Daily Telegraph, told BBC Breakfast that other members of the Royal Family, including the Duchess of Cornwall, had done the same in the past.
"Princess Anne is renowned for her frugality," she said.
"The fabulous thing is that the dress is a size 10 and 27 years on the Princess Royal is still wearing it. It's a body miracle."
A Buckingham Palace spokesman said the princess did not formally speak about her wardrobe choices.
BBC News website readers have been sending in their comments:
Like the princess said a well made suit will last you years if taken care of....... pity the rest of the fickle fashion industry doesn't do the same, instead of the waste we see today !!!!
Richard Parker, Newcastle Upon Tyne
It is quite an achievement that Princess Anne is able to fit into a dress that she wore so long ago - I wish that I could still fit into my waistbands from 27 years ago! And her frugality seems to sit well with her long-term involvement in the work of development charities overseas - congratulations on the weight control AND on the consistency of ethics too.
Sally Seed, Penrith, Cumbria
I don't wear the same clothes from twenty years a go as I was only 10, but I do still wear a lovely sheep skin jacket my dad bought for my mum when she gave birth to me. I also have a great orange leather jacket that belonged to my great aunt who died before I was born. But my best hand me down is a black suit jacket that my gran wore on her wedding day, she got married just after WW2 therefore she had to collect rations to get her outfit so wanted something she would get more use out of than a white dress, she got her wish as almost 60 years it is still being used and looks great. I like all these things not just because of the way they look but also they have a story behind them. Some things just never go out of date.
Caroline O'connor, Glasgow
Bravo, I think that's brilliant
Blu, Northolt uk
I wish! People moan about the Royal Family wasting tax payers money, and then seem to poke fun at them for wearing something, quote your text, "dug out" of their wardrobes after 27 years. Good for Princess Anne, if only others were as frugal. I wish things I got into 10 years ago still fitted me, let alone 27 years!
Helen Charman, Littlehampton
During a clear out, I found a pair of jeans that I used to wear back in 1987 when I was 19. Like the princess, I was rather chuffed that I could still get into them - however the "snow wash" finish is no longer fashionable so I think if anything they will be used for washing the car and clearing out the attic.
Sarah Halsted, Horley, Surrey
I WISH I could still get into clothes I wore 27 years ago. She's a very lucky lady that she can. I think it conveys a good message of not being wasteful, elaborate or a clothes horse. Good for her!
I have no problem with Princess Anne recycling clothes from years gone by - in fact, I think it admirable in this throwaway society. However, the dress in question was a fashion disaster in 1981 and is no less of one today!
So what? Haven't you worn something twice?? At least she's not wasting a good dress, and it still fits her. Good one you Princess!
Good on you Princess Anne. It looks great and why waste money (even if you do have oodles of it!) The only Royal with good sense (apart from the Queen). I wish Anne could be the next Monarch.
Go, princess Anne, go! The dress is back in fashion now...and it still fits her. Marvellous!
Isabella Jackman, Germany
Yellow is very in this year. If she was wasting money, we'd soon be complaining. At least unlike the pretenders, she is a princess though.
Richard White, Salford, UK