Her duty was to produce an heir to the throne.

她的任务就是生育王位继承人。

《牛津词典》

It's only the second time a potential heir to the throne has married a commoner.

这只是第二次王储与平民结婚。

《柯林斯英汉双解大词典》

At the time, the designated heir to the throne was ruling Navarre, a small kingdom in the Pyrenees Mountains.

在同时，王位的指定继承人正在统领比利牛斯山脉下的一个小国家——纳瓦拉。

youdao

The church bells ring very,very slowly,all over the place, because there is--the heir to the French throne is dead.

在各地,教堂的钟声非常缓慢地响起,因为王位的继承人去世

耶鲁公开课 - 1871年后的法国课程节选

We decided to come because we'd never have a chance to see the heir to the throne married again.

BBC: Royal wedding: Tears and tiaras in crowd on The Mall

Irish President Mary McAleese welcomed the heir to the throne at her official residence in Dublin's Phoenix Park for lunch.

BBC: Prince speaks of Irish 'suffering'

One of his sisters, another possible heir to the throne, is more popular, but Thailand has never been ruled by a woman.

ECONOMIST: Thais are impatient for change, but it will take time