Penny Lancaster and Kimberly Stewart experienced a real "motherhood bonding moment" after Stewart, 46, gave birth to her first child.Rod Stewart's wife confirmed on the "Postcards from Midlife" podcast that she stepped in to help when Kimberly had difficulty producing enough breast milk in 2011 to feed her newborn, Delilah. The British supermodel, who had given birth to her second son with Rod just six months before, was happy to help, and further clarified that she provided the milk, but did not breastfeed her granddaughter.ROD STEWART'S WIFE SAYS SHE WOULD HAVE LEFT HIM IF HE REFUSED TO HAVE CHILDREN"Not quite breastfed," Lancaster said. "Gave breast milk."Stewart and Lancaster share two sons together, Alastair, 19, and Aiden, 14. The "Forever Young" singer also has six children from four previous relationships, in addition to five grandchildren.ROD STEWART POSES WITH 4 MOTHERS OF HIS CHILDREN: 'A MOTHER'S REUNION!'Lancaster, 54, told The Times last week that she didn't question being able to help out her husband's oldest daughter."It was a real motherhood bonding moment," she told the outlet. "The breastfeeding nurse said, 'In a perfect world, you'd know someone who's breastfeeding' – and everyone turned to look at me."LIKE WHAT YOU’RE READING? CLICK HERE FOR MORE ENTERTAINMENT NEWS"I remember thinking, 'What's the most important thing for this child?' I knew my milk would give her the nutrients and antibodies she needed."Lancaster, who married Stewart in 2007, admitted that having children was a non-negotiable for her future plan with the "Maggie May" singer."Yes [I would have left him]. And that would have been very hard," she told the British outlet Saga magazine. "But we just went with the flow. Now Rod always says, ‘I wish I’d said yes [to babies] earlier, because then we could have had more children.’"CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTERAs recently as five years ago, Stewart and Lancaster considered adoption, but "it ended up not happening." She explained, "We thought there might be too much of an age gap."Lancaster joked that she's actually a mother of three, referring to Stewart as "a big baby who needs my attention in a different way.""I think all women would say that about their husbands," she told the outlet.Fox News Digital's Lauryn Overhultz contributed to this report.