The Queen expressed her delight about the expected arrival of her ninth great-grandchild.
She and husband Prince Philip are said to be “aware and delighted” at the happy announcement.
Mike was unwilling to reveal much about the baby’s due date, but it can be expected the baby will arrive in 2021.
Mike said: “We like to play our cards close to the chest.”
He added: “We haven’t told Mia yet because we knew she would tell everyone at school. Now that we’ve gone through the scan, yes (of) course we’ll tell her.
“She’ll be happy about it, she’s been requesting another sister or brother, so we’ve hopefully fulfilled that role for her. She just wants something different now.
“Lena’s growing up – she’s two-and-a-half now – she wants something younger to play with and dress up!”