Craig played DI Matthew "Dot" Cottan in the first three series of the hit BBC police drama.
The incident reportedly took place outside the studio where the former Hear'Say star presents her Smooth Radio show.
Fans can't agree on what the message means – or whether it's a red herring.
"It happened overnight. I went from being a girl to the mother to beyond the mother.”
The couple, who met in 2017, welcomed a baby boy earlier this month.
Following the Duke of Edinburgh's death the BBC wiped its schedules across both BBC One and BBC Two.
The Britain's Got Talent judge is following in Nigella Lawson and Lorraine Kelly's footsteps.
The former ITV breakfast presenter suggested starting a new show called Morgy And Fergie In The Morning together.