Justin Timberlake's marriage is ''hard going'', says his grandma.

The singer-and-actor and wife Jessica Biel - who he wed in October 2012 - spend a lot of time apart because of their respective careers and his grandmother Sadie Bomar is worried the distance is going to damage their relationship.

She said: ''They are married but they are so busy, both of them, it's hard going.

''I'm sure when it's right to have children they will, but not now.

''They do love each other dearly but they are apart so much it's going to be hard going for them.''

Sadie says Jessica finds the distance particularly ''tough'', but she is hopeful the couple can overcome their problems - so long as they make more time for one another.

She added to The Sun newspaper: ''I think Jessica finds that really tough. She's on her own a good deal.

''If he's not coming back at night that puts a strain on things, of course it does.

''It's hard to keep it all going but you have to have faith to keep it all going.

''I have faith in them and I believe they love each other dearly but I know they need time together.''