I Married my Kid Sister -Ortis Wiliki

Ortis Wiliki who just marked 30 years in the music industry made a shocking revelation. Unveiling the secret of his 20-year marriage to popular actress and singer, Becky, he told Punch , 

“I married my kid sister – my mother’s last born. We are as close siblings can be. That is why we have stayed together for this long.”

Could this be a figure of speech? Don't get it