London - Serena Williams describes elder sibling Venus as "the perfect sister" and her "best friend".
Venus calls her top-ranked sister "the ultimate champion" and reveals they "never argue."
So is there anything the world's most famous sporting siblings - who own 27 grand slam singles titles between them - don't like about each other?
"Her dog. He is bad," grinned Serena after she trumped her sister in the Wimbledon fourth round on Monday to move within three wins of holding all four majors at once.
"He kind of uses me, yeah. Whenever she comes home, he goes back to her. Kind of gets me excited.
"Been talking to her about that, though.
"Venus does nothing wrong. She's like the perfect sister."