It wasn't only the stunning Downton actress's pretty face the snappers were keen on documenting.
Her sleek, vintage Chado Ralph Rucci gown also revealed a seductive expanse of oh so trendy side boob.
To wear with aplomb - and to avoid the dreaded (whisper it) so-called Spaniel's Ear syndrome, the breasts must be on the smaller side of a handful, and be devastatingly pert.
She is a woman who cares not a jot if her side boob is droopy, and we love her for it.
Firstly, be realistic. If your breasts are much beyond a C cup, think twice. Assess your assets.
Women with DD-cups and above should only attempt the flash of side boob if their breasts are a) envy-makingly pert for their size, or b) hoisted up with the kind of intricate rigging that would keep a galleon on course.
There are ways and means to ensuring side boob success.
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First, choose your dress. If you are youthful/blessed with perky breasts, you can go for the big reveal. If not, choose a dress with perhaps a flash of rib, or that reveals the upper part of the side boob for a more subtle take on the trend. There are dresses that are cut out to reveal bare flesh, and those with netting that offer a more demure take on the look, like Michelle's
The popularity of Stella McCartney's panel dress over the past two years has spawned countless copies which are available across myriad high street stores, and the S/S13 catwalks were full of frocks with sheer panelling. This is one trend it should be easy to hunt down on the High Street.
Look for halternecks with cutaway sides, backless styles and mesh panelling.
Posture is key when the side boob is on show. Hunch forward or round your shoulders and your breasts will naturally droop, giving even perky girls a spaniel's ear effect..
This is the time to stand tall, throw your shoulders back, and thrust your chest forward... all damn night.
Keep it in mind at all times: the moment when you're slouching down in your chair looking into your gin and tonic is the moment your side boob will suffer. And no doubt the moment someone will take your photograph.
THE RIGHT UNDERWEAR
The side boob is a look that really lays the breasts bare, in more ways than one. There is little you can do to give really dramatic uplift without resorting to a bra - which destroys the effect.
But, there are techniques that can help. Stylists have a way with tit tape that can create uplift without wearing a bra. It takes a crosshatch-style application of the tape, also euphemistically named fashion tape, that actually pulls the breast upwards and tapes it higher up on the body.
Position the tape judiciously to ensure nothing is visible on the sides.
Modesty first: Nudwear's Nud Nips nipple covers will stick over nipples to help keep things demure when you're going bra-lessALSO TRY:
Nud bra, £48.99, nudwear.com
Sticks on to create the ultimate cleavage when you're going sans brassiere - and will have the additional benefit of pulling the breasts slightly upwards and together so they don't droop down tot he sides.
Especially good if your side boob dress is a halter style with a plunge - you get the best of both worlds: pert side boob and impressive cleaveage. Rinse and reuse again and again.
Fashion tape, £7.50, nudwear.com
Pull the breast upwards with your hands and literally tape it into place higher. Use a criss-cross method to hold the tape in place.
Nud Nips, £11.50, nudwear.com
Going bra-less, if you dare, or if you can - is all very well, but can land you with a new problem: Embarrassingly visible nipples. Wear these pasted over the top for modesty. They can be rinsed and reused over a hundred times.
THE RIGHT ATTITUDE
As mentioned before, Nancy Dell'Olio may not have the pertest pair in town, but she dresses with confidence, she is glamorous and groomed, and she has bags of charisma.
If all else fails, do a Nancy. Make gravity your friend and tell the world you don't care if you don't have the breasts of a 22-year-old.
That is almost as sexy as possessing the pert pair in the first place.
HOW TO DO SIDE BOOB LIKE A STAR... BUT AT HIGH STREET PRICES
Aqua trousersuit, £130, aquabyaqua.com
Black slip dress, £125, Ganni at my-wardrobe.com
Violet silk satin dress, £38, motelrocks.com
Red dress, £128, threefloorfashion.com