That is to say: There's a lot of pressure on these two to make it work. Will they?
Before we get into any predictions, it's important to note that no one can say with absolute certainty whether an individual couple will have a successful marriage, or whether they'll get divorced. The findings and observations below apply to couples in general.
That said, here's what the science has to say about the future of a couple like Prince Harry and Markle:
Markle is 36 years old; Prince Harry is 33.
According to Nicholas Wolfinger, a professor at the University of Utah, the odds of divorce are relatively high for couples who get married in their teens or after age 32. After age 32, Wolfinger found, your odds of divorce increase by about 5% every year.
Markle's parents, Doria Ragland and Thomas Markle, divorced when Markle was six years old. Prince Harry's parents, Prince Charles and Princess Diana, when Prince Harry was 11. (His mother died in a car crash the following year.)
As Business Insider's Rebecca Harrington reported, experiencing divorce as a child isn't exactly what predicts breakups later on. Instead, according to a 2015 study published in the journal Marriage and Family Review, kids who experience lots of family conflict are more likely to divorce as adults.
In other words, if parents get divorced and things subsequently calm down in the household, kids could fare better than if their parents stay married and continue to fight.
It's unclear how much family conflict Markle and Prince Harry experienced when they were younger, so it's hard to infer much from the fact of their parents' divorces.
Markle was previously married, to film producer Trevor Engelson.
Research suggests that second and third marriages are more likely to end in divorce than first marriages. There are a number of potential reasons why. For example, someone who survived one divorce may be more likely to initiate another, since it's not as scary. "It’s now the 'devil you know': if you’ve been through it once before, you know you can do it again," marriage and family therapist Virginia Gilbert told HuffPost.
Markle and Prince Harry were much more affectionate during their engagement interview than both Prince William and Kate Middleton and Prince Charles and Princess Diana. They held hands, giggled, and gazed lovingly into each other's eyes. By contrast, the other two couples barely touched or looked at each other.
One study, published in the journal Interpersonal Relations and Group Processes in 2001, found that this type of behaviour tends to predict the dissolution of the relationship. The authors write: "As newlyweds, the couples who divorced after 7 or more years were almost giddily affectionate, displaying about one third more affection than did spouses who were later happily married."
It's so important that we'll say it again: There is no Magic 8 ball for any marriage. There are myriad factors that predict a couple's happiness and stability, way beyond the ones we've covered here.
It's also worth noting that Prince Harry and Markle appear to be on the same page when it comes to their values and goals, which is important for any relationship.
In their engagement interview, Markle said, "It was really one of the first things we connected on, it was one of the first things we started talking about when we met, was just the different things that we wanted to do in the world and how passionate we were about seeing change.