In pictures of the pop singer taken at last night's Brit Awards, White's nipples can be seen clearly through her black top top.
Speaking about the incident on Twitter this morning, the girlband star said: "Oh god I've seen pictures from last night today and I am mortified! I honestly didn't realise how see through it was when I got dressed.
"I'm sorry if I offended anyone! No one wants to see that. lol. Ouch!"
She added later: "And the camera flash made it so see through! Cringe."