The new baby would join big brother Archie, 2, and sister Lilibet, almost 7 months.
“Harry and Meghan have done a lot of soul-searching about this,” says a source.
“They feel they can contribute more positively to the world by raising smart, informed children who will go on to be the same into adulthood. They feel the positives of that outweigh the risks to the climate.”
Currently, the plan is to start undergoing IVF when Lili turns 1 next June, depending on if Meghan, 40, is comfortable weaning her onto a bottle by then.
But what of their defiant pledge to limit their family planning to just two offspring?
“Of course, it’ll be slightly awkward, but they’ve learnt over the past couple of years that they can pretty much say whatever they want and get away with it, because the news cycle moves so fast.
“All they have to do is break the news of a third pregnancy, and then have another controversial news story to drop a week later and watch everyone move on.”
At the end of the day, say sources, Meghan and Harry have enjoyed being parents more than they could’ve dreamed and aren’t willing to put their baby years behind them just yet.
“Meghan absolutely loves watching Harry with Archie and Lili. He’s a natural-born father and, despite it all, when he’s with his kids it’s the happiest he’s ever been,” concludes the source. “Meghan can’t bear that this is the last she’ll see of him with a newborn.
“Plus, ever since Lilibet arrived, Archie has been asking for a baby brother – and neither Meghan nor Harry can ever say no to him!”
Read more in this week's New Idea, on sale now.