The former Made In Chelsea stars tied the knot in a lavish ceremony last year.
Now Mackintosh, 30, has told Hello! magazine that she is 14 weeks pregnant and expecting a girl.
"Hearing her heartbeat for the first time with Hugo by my side was one of the most amazing moments of my life so far," the fashionista said.
"I feel very lucky. I can't wait to feel that bond and for her to sleep on my chest and breathe in that baby smell."
She said of seeing her baby in a scan: "She's got long legs. Hugo thinks she's going to be really tall like him.
"I'm so excited it's a girl. I would've been delighted with either, but when I found out we were having a girl, I suddenly realised this is what I really wanted."
Mackintosh, who was previously married to Professor Green, said she has been preparing for motherhood by babysitting the one-year-old son of Spencer Matthews and Vogue Williams.
"Theodore is so sweet. It was hard when he cried and we were so relieved when he settled down to sleep," she said.
But she added: "Everyone says it's different when it's your own."
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Mackintosh, whose family created Quality Street, and Taylor dated in 2011 while on Made In Chelsea before splitting up.
They reunited in the second half of 2016 and Taylor proposed during a holiday in Greece.
Mackintosh married rapper Professor Green in 2013, but the pair announced their split in 2016.
The full interview is in the latest edition of Hello!