There's something about Meghan: her behaviour during her Irish visit will impact how the world sees her
Meghan will charm us all when she visits this week and start the process of winning over the world as the second Diana, says Sarah Caden
According to the Cambridge English Dictionary, the definition of synergy is "the combined power of a group of things when they are working together that is greater than the total power achieved by each working separately".
In celebrity terms, synergy can work for a celebrity plus a brand (think Clooney and Nespresso) or for celebrity couples, who are even more powerful as a pairing than they were solo (think Posh and Becks).
In the case of Meghan Markle and the Windsors, it is as yet unclear how the celebrity synergy will play out, but this week's trip to Dublin might well prove an indicator. Thus far, it seems an equally mutually beneficial meeting of new- and old-world stardom, but that could easily shift.
As Harry and Meghan launch themselves as a married couple in to world tours, with Dublin as a part of a gentle introduction, how she wows the masses will start to set the tone for their partnership.
The manner in which Meghan manages herself on world tours could be what decides whether she becomes Diana Mk 2, in terms of universal affection and super-stardom, or whether she settles into a role as Kate's also-ran sister-in-law.
We've never been massively bothered that Harry's never called to visit before and we'd hardly be this excited about his impending arrival if Meghan wasn't with him. Certainly, she's the one that Irish eyes hope to catch a glimpse of.
Which is all great for the fairytale so far. Actress of humble beginnings and mixed race lands herself a prince and becomes a bona fide princess. She's hit the happily-ever-after jackpot and isn't she a lucky girl.
Of course, the house of Windsor gains from this union too. The international attention paid so far to the story of the actress and the prince has been unprecedented and has mostly reflected well on the royals.
They've been so welcoming of Harry's choice of bride, a girl not only from America but from the world of showbiz, too. A girl with a fractured family; a girl whose dad couldn't turn up for the wedding, thus allowing Prince Charles to gallantly rise to the occasion. They've been warm and modern and compassionate and all those things that for years - particularly after Diana's divorce from Charles and her later death - they were accused of lacking.
So far, Meghan's been portrayed as a damned lucky Yank, while the royals have reaped the brownie points and seen their popularity soar.
So far, the Windsors are the ones doing best out of the union, but that may simply be because Meghan remains in the rehearsal phase of making this new role her own.
At the moment, neither the royal family nor Meghan really have a handle on what they've entered in to. She is, without doubt, nothing like Kate Middleton, who is the kind of girl that aristos can get their heads around. Much has always been made of Kate being middle-class, but all that really amounts to is that her parents don't have titles and earned their millions rather than inherited them.
She went to the right schools, met the right people and didn't end up with William through some sort of prince-and-the-pauper circumstances. They met because they had mutual toff friends and moved in toff circles at St Andrews University. She is one of theirs.
Kate has also been on the Windsor scene since her late teens, so she not only grew up getting their world, but she grew into adulthood adhering to the etiquette and arcane rituals.
By the time Kate married William, she was an old hand at the royal thing and she has rapidly matured into being a stalwart of their set-pieces and stuffy visits and walkabouts.
The whole shooting match is a new world to Meghan Markle and her apparent nervousness at the public appearances she had made with Harry have probably partly been cluelessness. She's playing a part; but she doesn't know the lines and the moves yet. And the scrutiny, which isn't a feature of the rehearsal period of the acting world, is relentless.
In recent months, she has had the quality of her curtsies to the Queen picked apart; her hand-holding with Harry; the crossing of her legs in the Queen's company; her too-pale nude tights. No wonder the girl has, to date, looked ill at ease in public.
The scrutiny of her family hasn't helped, of course. Her father's appearance on Good Morning Britain, in which he commented on her marriage, was reported to have led her to believe that severing ties was the only answer to keeping the royal peace.
Then, only last week, one of Prince Charles's friends, the designer Nicky Haslam, called the Markles "frightfully common. It would have been awful if that huge lump [Meghan's father] had been there. The royals probably don't quite know how to deal with them".
Well if we needed anything more to endear Meghan to us, the mere mention of "common" has done it. There's nothing we like more here than someone putting it up to the toffs.
Thus far, we warm to how she seems slightly ill at ease at royal events and get a bit of a giggle out of how Harry had to tell her to look up as planes performed a flyover at the recent Trooping of the Colour. Kate was like one of the Famous Five, marvelling as if she'd never seen an aeroplane before, but Meghan seemed sort of baffled by the fuss, as any of the rest of us would be.
And we will welcome Meghan this week as one of our own. There's Irish ancestry, apparently, but it's more than that. We have a simpatico with Meghan, while Harry, for all his modern openness will remain other to us. Meghan, however, we get.
In the synergy stakes, everyone is doing well from the marriage of Meghan and Harry so far. As she learns the ropes and the role, however, Meghan remains something of the lesser partner. Her status is boosted by association with him, the balance of power still rests with her in-laws.
As an actress, though, she will quickly master her part and what we see next week, in the rather more relaxed environment of Ireland, might be the star that Meghan has been in her life before Harry.
That star quality, too, may come to the fore as she becomes more comfortable. She has, without doubt, an easy charm with people that we haven't seen since Diana and as she grows in confidence that may be the Meghan we see more of.
As that unfurls, then, the Windsors may well realise that the perception that they have embraced Meghan is all wrong. In truth, in time, it may become the case that the royals are really living in Meghan's world.