"OMG Dad to be AGAIN :)) Brilliant," he wrote on Twitter on 26 May. "So, so happy."
Andre has never shied away from revealing he wanted more children with MacDonagh, stating he didn't want to be "changing nappies at 50".
"I have to wait for Emily to say yes," Andre told OK! Online during the NTAs in January 2016.
"It might take some time."
Qualified doctor MacDonagh, who married Andre in July 2015, has previously said she was keen to focus on her career before trying for baby number two.
She told OK! Magazine in October 2015: "I really want to see how my work's going... it's quite difficult for me as I love my time with Millie and I feel we have such good one-on-one time."
Congrats to the couple!