In the new annual Hot Bodies issue of Us Weekly, new mom Christina Aguilera — who welcomed son Max in January — shares the diet and workout secrets behind her 40 pounds weight loss .

In the interview, she also finally addresses the famous growth in her chest that came from breastfeeding.

“It’s kind of hilarious! I’ve never fit into an E-cup before,” she tells Us. “I look at my husband and go, ‘Guess what size this bra is?’ And when I tell him, he’s just amazed. We keep the tags that prove it, to look back for memory’s sake!”

For more on the best diets this summer and interviews with this year’s Hottest Bodies, including Kelly Ripa and Fergie, pick up the new issue of Us Weekly, on newsstands now.