Despite their agreement after Megxit that he would no longer use that title, Prince Harry described himself on his daughter’s birth certificate as “His Royal Highness.”
According to the papers acquired by The Sun, Prince Harry’s first name is “Duke of Sussex,” and his last name is “His Royal Highness.”
It drew attention since Prince Harry, 36, and his wife Meghan Markle, 38, had decided to discontinue using their “HRH” titles in January of the previous year. This decision was taken shortly after they announced their desire to quit as senior royals.
According to The Sun, even though they were no longer using the titles, they were never really revoked.

The newspaper said that Rachel Meghan Markle didn’t care about formality and called herself by her full legal name. 

Rachel, the former “Suits” star’s true first name, was disclosed when she listed herself as “Rachel Meghan, Her Royal Highness, The Duchess of Sussex” on the birth certificate of her son Archie, who is now two years old. This event made national news.
This is a copy of Archie Harrison Mountbatten’s birth certificate, which was made at London’s Portland Hospital. 

On that specific certificate, her title was listed as “Princess of the United Kingdom.”
Lilibet Diana Mountbatten-Windsor was born on June 6 at 11:40 a.m. at the Santa Barbara Cottage Hospital, which is near the family’s estate, according to the most current paperwork generated in Santa Barbara.