It is a marked difference, for example, from the queen, who has maintained a more traditionally aloof style.

Prince Harry and Ms. Markle are expected to be known as the duke and duchess of Sussex after they are married, according to the British news media, although she may be known informally as Princess Meghan. If Prince Harry were to decline the dukedom, he would remain Prince Henry of Wales — his official name.

The pair have dated for more than a year, and made their first official outing together in September in Toronto at the Invictus Games, a Paralympic-style competition for wounded or sick members of the military and veterans.

Like his brother, Prince Harry grew up in the public eye, first as a son of the heir to the throne, and then as an adolescent struggling over the loss of his mother, Princess Diana, who died in a car accident when he was 12. His grief played out in what he described as “total chaos” in his 20s, a period that was gleefully pounced on by the tabloids.

The relationship of Prince Harry and Ms. Markle also has been the subject of intense scrutiny.

The announcement of their engagement ended days of fevered speculation by the British news media, some of which, in anticipation of the event, tried to find any royal connection with Ms. Markle. (The Daily Telegraph breathlessly reported an unverified study showing that Ms. Markle’s ancestor was an aristocrat who was beheaded by Henry VIII, a distant relative of Prince Harry.)