Where is Zara Tindall's baby in the line of succession?

Watch: Zara’s royal baby boy Lucas born at home on the bathroom floor

The Queen's granddaughter Zara Tindall has welcomed her third child, a son with husband Mike Tindall.

They confirmed their baby is called Lucas Philip, with his middle name a nod both to his great-grandfather, Prince Philip and his paternal grandfather, Philip Tindall.

Although he is the great-grandson of the Queen, he does not have a royal title, because he would not be entitled to one in his generation.

This is because of a rule that's more than 100 years old - the 1917 letters patent said that the titles Royal Highness (HRH) and prince and princess should be restricted to the children of the sovereign, the children of the sovereign's sons, and the eldest son of the Prince of Wales.

Zara's mother, Princess Anne, also declined any royal titles for her children, with Zara and her brother Peter Phillips not having any earldoms or dukedoms.

That means Zara doesn't have a title to pass on.

Unlike his cousin Archie, the first son of Prince Harry and Meghan Markle, Lucas will never inherit a title, because Prince Charles is his great-uncle, not his grandfather.

Archie could become a prince when Charles accedes, under the 1917 letters patent rule, provided no other rules supersede it.

But, just because Lucas doesn't have a title, that doesn't stop him having a place in the line of succession, which shows how far away from the throne each Royal Family member is.

Lucas is 22nd in line to the throne, behind his older sisters.

Read more: Everything you need to know about the Queen's 18 grandchildren and great-grandchildren

However, he is so far down the line because of an older rule which was not changed until 2013, which meant women were knocked down the line of succession by younger brothers.

It means that his grandmother Anne, despite being the second child of the monarch, is behind her brothers Prince Andrew and Prince Edward, as well as their children and now grandchildren.

The law on male succession was changed just in time for the Duke and Duchess of Cambridge's first child, ensuring that if Prince George had been a girl, any younger brothers would not have been higher in the line than her.

However it's actually Princess Charlotte who is the first royal to benefit from the change in the law, as little brother Prince Louis stays below her.

And now Lucas's older siblings, Mia and Lena, also remain in line at 20th and 21st, despite having a younger brother.

Lucas's arrival also bumps down more members of the Royal Family.

This generation of royal babies are unlikely to ever be working royals, but it's the existing senior royals who are having to shift down in the line of succession as they arrive.

When the Queen started royal duties in the 1950s, she drafted in some of her cousins to help spread the load of work, because of an absence of appropriately aged children.

But as the years have gone on, her children have picked up duties, as have her grandchildren, with the cousins continuing to work too.

For example, the Duke of Gloucester, who carries out royal duties, was fifth in line when he was born, but is now 29th. He will be at least 30th in line by the end of the year.

Read more: Prince Harry says his family 'cut him off': Who gets security in the Royal Family?

As the new royals are unlikely to ever be working royals, they also won't automatically get any security, as that is decided by the government and the Metropolitan Police, for those who carry out duties.

The Queen is understood to be privately paying for security of some of the family members.

The top 10 in the line of succession remains unchanged by the arrival of Zara's baby, as it was unchanged by the arrival of Eugenie's child.

The next change to the top 10 will be in the summer when Harry and Meghan welcome their second child. That baby will be at eighth and will bump down Prince Andrew and his daughters.

The line currently reads the Prince of Wales, the Duke of Cambridge, Prince George, Princess Charlotte, Prince Louis, the Duke of Sussex, Archie Mountbatten-Windsor, the Duke of York, Princess Beatrice and Eugenie.

Watch: How the line of succession to the throne works