In an interview with Inside Soap, the programme's boss predicted that life will never be the same for the show favourites once the new arrival makes their mark.
Speaking of his plans for the McQueens, Marquess promised: "They're definitely staying! In fact, we're bringing in a new McQueen, who will change the dynamic of the family quite considerably.
"Jacqui in particular will go in a new direction, which is great as I think Claire Cooper is a very good actress."
Meanwhile, Marquess also hinted that fans will be surprised by what is in store for bubbly Cheryl Brady (Bronagh Waugh) and long-standing character Darren Osborne (Ashley Taylor Dawson) over the coming months.
He said: "I love Cheryl. Big things are happening for her - we're bringing in a very nasty man indeed to make her life a misery.
"I think Ashley Taylor Dawson, who plays Darren, is a really strong actor, and by the end of this year we'll see a very different side to his character."