The former England rugby player revealed on The Good, The Bad & The Rugby podcast that his wife Zara had given birth at home. He said that the couple's firstborn, seven-year-old Mia, was "over the moon" while Lena, two, declared that Lucas was "her baby".
Mike, 42, also revealed that his children had been elsewhere for the day as Zara, 39, had been having contractions through the night.
WATCH: Mike Tindall announces birth of baby boy
Their baby boy Lucas Philip Tindall was born at 6pm on Sunday, weighing 8lbs 4oz. The tot is the tenth great-grandchild for the Queen and the Duke of Edinburgh and is 22nd in line to the throne. His middle name Philip is a tribute to the Duke, as well as Mike's father.
Mike recounted the tale of Lucas's birth at home on the Gatcombe Park estate, saying on the podcast: "Sunday got even better because a little baby boy arrived at my house. 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."
Mike is also the proud dad of two daughters
The sports star also revealed that Zara's friend Dolly, who was present at the birth of their two daughters, recognised that they wouldn't have time to go to hospital.
"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," Mike said.
"The best thing about being at home, the best thing was, as soon as he's wrapped up, he's skin on skin, straight downstairs. TV room. Golf on. This is what we're doing," Mike added.
He also praised his equestrian and Olympic medallist wife Zara, saying: "As every man will say, she was a warrior as always, they always are."
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