The 29-year-old blonde beauty has been dating the legendary singer's son, Evan Ross, since June and he says his mother is a huge fan of his girlfriend.
The 25-year-old actor told UsMagazine.com: ''She loves her.''
Evan attended the premiere of his new film, 'CrazySexyCool: The TLC Story,' in which he plays music producer Dallas Austin, in Lincoln Square in New York City with Ashlee and his mother on Tuesday night (15.10.13).
He said: ''She's here. She's with my mom sitting down. I had them take her to a seat.''
Once insider the cinema, he sat between The Supremes star and Ashlee, and an eyewitness confirmed they all looked extremely close.
The source said: ''Diana kept talking over and around Evan to Ashlee laughing and chatting and they seemed very close. Diana and Ashlee seemed to get along so well and Evan and Ashlee held hands while they spoke to Diana before the movie started.''
The 'Pieces of Me' hitmaker, who is Jessica Simpson's younger sister, previously dated 'Boardwalk Empire' star Vincent Pizza for 18 months until November 2012.
She also has a four-year-old son, Bronx, with her ex-husband Pete Wentz.
There are currently five separate teams working on 'Game of Thrones' projects at HBO.
She's a big fan of the band and this week she got to perform with them.
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