Two of her female cousins, Princesses Beatrice and Eugenie, have royal titles. However, her other female cousin, Zara Tindall, is not a Princess either.
The reason lies in the fact that Louise's father, Prince Edward, became an Earl when he married his wife Sophie in 1999, and the couple agreed with the Queen that their offspring would be styled as children of an Earl rather than a Prince, perhaps because they are not the monarch's direct heirs.
WATCH: Sophie Wessex twins with daughter Lady Louise in a chic pink power suit
They are therefore known as Lady Louise Mountbatten Windsor and James, Viscount Severn. At 14, James, is now the only one of the Queen's grandchildren who is under 18.
The pair were given HRH titles at birth which they could choose to use when they turned 18, but so far, Louise has chosen not to do so.
Prince Andrew's daughters do use their titles, which is less typical for royals who are not working members of the royal family.
Louise is the Earl and Countess of Wessex's oldest child
However, the sisters do sometimes represent the Queen at events, such as Buckingham Palace garden parties.
In contrast, Princess Anne's first husband Mark Phillips declined the Queen's offer of an Earldom when they married and the couple preferred their children to not use titles, being known simply as Zara and Peter.
Speaking to Vanity Fair, the Princess Royal reflected on the decision, saying: "I think it was probably easier for them, and I think most people would argue that there are downsides to having titles. So I think that was probably the right thing to do."
The teenager inherited the late Duke of Edinburgh's carriage
It's possible that Louise and James could begin using royal titles in the future, perhaps when Edward becomes the new Duke of Edinburgh after Prince Charles accedes to the throne.
Their mother Sophie has previously spoken about her and her husband's down-to-earth attitude towards raising children, though, saying: "We try to bring them up with the understanding they are very likely to have to work for a living."
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