Mills already shares a daughter called Skye, who was born last July, with her husband.
“Skye’s going to be a big sister,” she said.
“We’re feeling so lucky to hold on to something so special while the world feels so topsy turvy, and whilst of course it’s a little unnerving to be navigating pregnancy in this climate, we are just so incredibly grateful.
“Like everyone else, we’re staying quietly at home, taking Austin and Skye our for a little daily walk on our own, which this morning was the quietest and emptiest I’ve ever seen London.
“Sending so much love to you all.”
Mills married Matthew, the son of the late Dame Tessa Jowell, in 2016, and the couple run the Deliciously Ella business together.
Deliciously Ella reveals she is expecting her second child