The 'Dancing With the Stars' champ goes under the knife on Tuesday (Oct. 28)

The source of Julianne Hough's stomach problems is now clear.

The "Dancing With the Stars" champ has been diagnosed with endometriosis and will also be undergoing minor surgery Tuesday (Oct. 28) to remove her appendix. Previous reports of an ovarian cyst were not mentioned.

"Everything's okay," said Hough, 20, on Monday night's show after she performed the samba with celebrity partner Cody Linley. "I'm going to hopefully be back, if everything goes as planned, next week."

In the meantime, Linley will partner with the previously booted Edyta Sliwinska for next week's routine.

"I'm sad that I'm not going to be with Julianne, but I'm happy that I'm with Edyta," said Linley.

Endometriosis affects about 5-10 percent of women of reproductive age and involves the growth of uterine-lining tissue beyond or outside the uterus, such as on the appendix.