Portia de Rossi’s ex-husband left her and broke up her brother’s marriage -- taking off with his wife, RadarOnline.com has learned.

“My husband left me,” Portia begins in her newly released memoir, Unbearable Lightness: A Story of Loss and Gain.

PHOTOS: Ellen & Portia's Romantic St. Barts Getaway

“When my husband left me, my brother moved in to my place... My husband ran off with his wife, so we kept each other company and we liked to go out for margaritas and Mexican food to commiserate.”