Justin Timberlake's grandma says he'll make "an amazing dad".

The singer's relative spilled the beans on what sort of father she thinks he'll be.

Sadie Bomar, who has opened up about the star in the past, says she's confident about Justin's paternal abilities.

Justin married actress Jessica Biel in October last year and Sadie predicts it won't be long until the couple start a family of their own.

"Justin is going to make an amazing dad," Sadie told British magazine Grazia. "They want a big family so I guess it won't be too long. They are the most lovely couple."

Sadie is the inspiration behind Justin's latest music video for hit single Mirrors. The touching tale, which the star tells through the song, follows a love story spanning six decades. This is based on the romance of Justin's grandparents, which Sadie says has been made all the more poignant as a result of her husband Bill passing away last December.

"I like the way he catches my wedding ring, like he's the husband now," Sadie explained while discussing the music video. "He's making a great husband. I am close to Justin and it was a lovely, beautiful thing for him to have done. That's how he is."