Sadie told the Radar: Yes, Justin is engaged.
There have been reports since Wednesday that the couple have recovered from the nine-month-long break-up and got together. The grandmother's words have confirmed them.
According to her, Justin and Jessica are yet to decide on the wedding location as it is too early to decide, but it may take place in Memphis or Colorado.
Jessica spent Christmas and the New Year with Justin and his parents in Montana and that's when he proposed to her.
Justin rang me himself on Christmas day to tell me about the engagement, she said.
Jessica is a very sweet girl, she's upright and everything and we love her. She's a wonderful campaigner for the environment and Justin is too, a fine young man. Jessica will be a lovely member of the family, Sadie added.
In 2009, when Justin and Jessica were going through a rough time of their relationship, the grandmother of the famous singer had given a statement: As far as we're concerned, he's always been single.... The girlfriends come and go, but we believe nothing has ever been serious.
But this time she is all open about her grandson's engagement and indirectly clarified why Justin took so long to propose Jessica.
You know Justin, he's a very laid back he was excited but he don't make a big episode out of anything. It just seemed like the right time for him I guess, she said.