London - The gathering had all the hallmarks of a girly celebration - smoked salmon bagels, gooey chocolate cakes and a gaggle of women giggling as a party planner showed them “sexy lingerie and bedroom toys”.

And no one was having more fun than the guest of honour, a middle-aged woman named Maggie.

Yet this wasn”t a birthday bash or hen night, but a party held to celebrate - or commiserate over - the fact Maggie’s former husband, to whom she’d been married for 30 years and separated from for ten, would that very day say “I do” to his new wife.

While this may seem odd to anyone who knows the sadness and bitterness divorce can bring, Maggie said that as soon as she learned of his impending nuptials, she knew she had to occupy herself, “and not sit home alone, thinking about the day we got married”.

Friends suggested many activities, from going on the London Eye with a bottle of champagne to hopping over to Paris for the day, but she plumped for a party at home - and turned what could have been a sad day into a raucously memorable one.

The question of what to do when your ex-spouse re-marries might not be easy to resolve, and yet it’s very important. Because how you choose to spend your ex’s wedding day could set the tone for the next phase of your life.

What would you do? Would you get drunk? Methodically cut up all his/her old photographs? Get on a plane to New York to max out your credit cards in Bloomingdale’s? Stick pins in a wax model?

This was the fascinating issue I discussed on the BBC’s Woman’s Hour with Jenni Murray recently, in a programme that generated a huge response from the public.

The item was prompted by a call from Maggie, a regular listener, explaining how she had to come to terms with the dreaded day by holding that risque party.

Equally feisty was Anna, another caller interviewed by the programme. On the day her ex was remarrying, Anna was on holiday with friends in California. She started the day with champagne, took a road trip to Yosemite National Park, drank shots of tequila, watched the sun set behind mountains, enjoyed a terrific dinner, then drove back to San Francisco after three days: “Where I then met the man I married a year later...and here I am living in the US.”

So three cheers for those two terrific women! Instead of going to ground to lick their wounds they burst from their lairs and defied any feelings of being left behind on the shelf.

Of course, this isn’t easy. I know nothing of what happened to end the marriages of Maggie and Anna, but that back-story is surely the key to how hard it is to save yourself from feeling miserable. That is certainly my experience.

The day my former husband (to whom I was married for 35 years) remarried was perfectly ordinary. I worked at my advice column, which was itself a good route to reflecting that he and I were actually lucky, compared with many of those who write to me.

Why so? Because there was no animosity, no bitterness in our relationship - and I certainly find plenty of that in my postbag.

For example, on January 21 this year, I published a letter from a “raw and angry” woman, divorced for nine years, who had chosen to miss her daughter’s wedding because her ex was going to be there with “his floozy”.

Seven years later, she has a new partner, but wrote: “I hate [my husband and his new partner] with all my heart.” This reminds me of the old Chinese proverb: “He who cannot forgive must dig two graves.”

In contrast, a man called Andy tweeted Woman’s Hour to say that not only had he attended his former wife’s wedding, but had given one of the readings. I find that so uplifting. If asked, I could also have performed such an act of reconciliation - though it would have been hard.

But arguably it’s a step too far - because the wedding day should be not only a new start for your ex, but for you, too. I don’t think I’d really want a walk-on role on someone else’s stage.

But I do believe you should do everything in your power to encourage the children of the marriage (whatever age) to go to the wedding, even if they don’t want to.

In the case of my family, this wasn’t up for debate. They love their father and so they would obviously go to his wedding - wishing him as much joy as I did myself. After all, what else is there to wish? Shakespeare expressed my feelings in the great line: “Love is not love which alters when it alteration finds.”

Of course, the individual case history is everything. My former husband was marrying a woman who had played no part whatsoever in the end of our marriage.

I, in turn, was living with someone else, whom I was later to marry, too. In those circumstances, you may feel nostalgic, confused and wistful (as I certainly did) on the day your ex remarries - thinking back to your wedding day, with its shared expectations of a long life together. Yet you are spared corrosive resentment - or, at least, you should be.

How different it is when the happy new bride or groom is the very person who caused the break-up of the marriage. Then the one left alone can be forgiven for feeling a spurt of savage rage and the sense that the other person has finally “won”.

And the wedding day rubs cruel salt in the wound. The agonising, on-going sense of betrayal and injustice is hard to endure. This is the real test. In these (all-too-common) circumstances I’d counsel the “wronged” one to do anything possible to avoid lurking at home feeling angry and/or miserable.

If you can, go to another time zone (like Anna in California), so it’s hard to look at your watch and brood, thinking: “It’s happening now.”

Taking off with a good friend, joining a singles holiday, doing something out of character such as joining a Ramblers Association day out...such things can be essential methods of self-preservation.

This will sound bizarre, I know (especially to those who are very angry), but I believe the most liberating thing you can do, just before your ex marries someone else, is to post a wedding day card. While this may sound mad - or at best impossibly idealistic - such an action enables you to take some small measure of control.

Even if you don’t really mean it, even if you want to stab your pen through the card and spit angrily on the stamp, you’re saying “No” to being a victim.

The very act of taking a deep breath and writing “good luck today”, then posting the card, enables you to take a giant step out of the mire that’s imprisoning your feet. It says: “Whatever you did to me, I am damn well bigger than what happened.”

Because you have to be - for the sake of your own survival. If you reject all such suggestions, choosing instead to clutch pain to your chest for ever, you’re taking yourself down.

It’s you, not your ex, who is responsible for misery. Yes, you may have been wronged, but in making bitterness a way of life you are compounding that wrong. Confetti will rain down on the happy pair of newly-weds while you are drowning in your own tears.

Why should you? I don’t think any of us owe our identity to being one half of a couple. You were your own self before you said “I do” all that time ago - and you are still that person, with one precious life to live.

On the day your former spouse makes their vows, the bravest, most sublime thing you can do is to shout “I will” to yourself - saying yes to a fresh start, a new life. - Daily Mail