The former Oasis band member, 46, told Britain's Sunday Mirror newspaper he felt obliged to ask his sibling to the ceremony for the sake of their mother, explaining: "Of course he will (get an invite). My mam is like, 'You've got to invite him.' And I will. They'll get a little envelope through the door."
"They won't come..." the "Wonderwall" hitmaker insisted. "But you never know – like I said before, they go to the opening of anything so as soon as they open it, it'll be like, 'Come on Noel, get your Dermot O'Leary outfit on, we're going out'."
News of the couple's reported engagement emerged earlier this month, and Liam detailed how he proposed to Debbie while they were having a drink, after suggesting "for ages" that they tie the knot.
Adding that he's "third time lucky" in love, the "Don't Look Back in Anger" star suggested he'd finally found the one, following his failed marriages, first to actress Patsy Kensit and then singer Nicole Appleton.
"I'm buzzing more than her. This one's going to be a big thing. She is top, man. She is my little Yoko," Liam gushed.
The former Oasis singer regularly topped the charts with his brother Noel, 52, from 1991 to 2009, when their ongoing feud came to a head and the duo finally called it quits.