Prince Harry and his wife Meghan announced on Wednesday that their daughter was christened in a private ceremony in California, officially referring to her as a princess and announcing for the first time that they will give their children royal titles.

Princess Lilibet Diana, who will turn two in June, was baptized on Friday by the Archbishop of Los Angeles, the Rev. John Taylor, according to a statement released by Harry and Meghan. Afterwards, the titles of Lilibet and her four-year-old brother Archie will be posted on the Buckingham Palace website.

The announcement marked the first public appearance of the children's titles.

Two years ago, during Harry and Meghan's television interview with Oprah Winfrey, the subject of the children's names took centre stage. Meghan, who is biracial, stated that while she was pregnant with Prince Archie, "they" — presumably the palace — "were saying they didn't want him to be a prince ... which would be different from protocol."

Meghan speculated that this was because Archie was the "first member of colour" in the royal family and would have been the first time a royal grandchild was not given the same title as the others.

Royal scholars stated that Meghan's remarks appeared to be based on misunderstanding of how royal titles are bestowed.

By a proclamation signed by King George V in 1917, the titles of prince and princess were restricted to the male-line grandchildren of the monarch.

As long as Queen Elizabeth II was alive, Princes Harry and William were the monarch's grandchildren. Being great-grandchildren, Harry and William's offspring did not obtain the titles immediately.

But, Elizabeth had the authority to change the regulations, and in 2012 she ruled that Prince William and Catherine's children would be princes and princesses. This order did not apply to Harry and Meghan.

In September of last year, however, the situation altered when King Charles III gained the throne upon the death of his mother. Because William and Harry are the king's sons, their children are now royal grandchildren and so entitled to the titles of prince and princess.

Yet, they have remained "master" and "miss" for the past six months on the Buckingham Palace website.