Katharine McPhee is clearly smitten with her 7-month-old son, Rennie David Foster, and she didn’t hold back in describing the absolute “heart explosion” she feels for him in an EXCLUSIVE interview with HollywoodLife.com. “I mean, just everyone talks about it, but the love that you have, it just is like a heart explosion,” she gushed. “Maybe if I’d had a baby in my early 20s wouldn’t feel this way. But just really, nothing else matters.”