It’s not easy to upstage a 141-year-old Tiffany & Co. diamond, but Lady Gaga managed to do just that in a makeup-free selfie she posted on Instagram yesterday. The Oscar winner’s ridiculously glow-y complexion had hundreds of commenters wondering, What’s Gaga’s skincare routine?

Luckily, Lady Gaga’s makeup artist, Sarah Tanno, recently spoke to Refinery29 about the beauty products she uses on the star. Tanno revealed that one must-have product is a good vitamin C serum, which is no surprise: Dermatologists rave about vitamin C’s potent brightening powers, and the ingredient can do wonders to lighten dark spots and give skin a lit-from-within glow.

Tanno’s go-to vitamin C serum is Ole Henriksen Truth Serum ($48; sephora.com and amazon.com), which happens to be one of our favorites too. In a previous interview with Health, New York City dermatologist Debra Jaliman, MD, noted that in addition to vitamin C in the form of 10% sodium ascorbyl phosphate, the formula packs other good-for-skin ingredients like hyaluronic acid and green tea extract.

Credit: Instyle