Zara and Mike Tindall have announced the birth of a son, who they have named Lucas Philip Tindall.
A spokeswoman for the Queen's granddaughter and the former England rugby player said their third child was born on Sunday, weighing 8lbs 4oz.
The baby was born on their bathroom floor after they were unable to make it to hospital in time, Mr Tindall said.
The Queen and the Duke of Edinburgh are "delighted" at the news, Buckingham Palace said.
They "look forward to meeting their 10th great-grandchild when circumstances allow", a spokesman added.
The child is 22nd in line to the throne.
His middle name is in honour of both Mr Tindall's father as well as Mrs Tindall's grandfather.
Mrs Tindall, 39, and her husband already have two children - seven-year-old Mia and two-year-old Lena.
Describing the birth on his podcast, The Good, The Bad & The Rugby, Mr Tindall, 42, said: "Arrived very quickly. Didn't make it to hospital. On the bathroom floor."
"So yeah, it was running to the gym, get a mat, get into the bathroom, get the mat on the floor, towels down, brace, brace, brace," he added.
Mr Tindall said his wife's friend Dolly, who was also at the birth of their two daughters, "recognised that we wouldn't have got to hospital in time".
"Fortunately the midwife who was going to meet us at the hospital wasn't that far away so she drove up just as we had assumed the posit [position] and the second midwife arrived just after the head had arrived," he added.
Their other two children were elsewhere for the day because Mrs Tindall had been having contractions through the night.
Mr Tindall said Mia was "over the moon" and Lena had declared Lucas was "her baby".
It comes just a few weeks after Mrs Tindall's cousin Princess Eugenie had her son August.
Mrs Tindall, who is a medal-winning equestrian, is the daughter of Anne, the Princess Royal - the Queen's only daughter.
In 2018 she spoke about her experience of going through two miscarriages before becoming pregnant with Lena.