Harry and Meghan’s baby is believed to be due in late April.
The Queen celebrates her birthday on April 21, while Louis will turn one next year on April 23 – patriotic St George’s Day.
If Meghan goes overdue, she might even welcome her baby on the same day Princess Charlotte was born – May 2.
Meghan has had her 12 week scan, suggesting the baby was conceived only around 10 weeks after the duke and duchess’s Windsor wedding in May.
The baby is expected to arrive around 11 months after Harry and Meghan’s wedding – and before their first wedding anniversary on May 19.
This follows in the footsteps of Harry’s parents Diana, Princess of Wales and the Prince of Wales.
Harry’s older brother Prince William, now the Duke of Cambridge, was born in June 1982 – 11 months after Diana wed Charles in July 1981.
The Duke and Duchess of Cambridge’s first child Prince George arrived two years and three months after they wed.
But the Queen, then Princess Elizabeth, welcomed Charles in November 1948, a year after she married the Duke of Edinburgh in November 1947.