Ashlee Simpson Engaged to Diana Ross' Son Evan

Ashlee Simpson, younger sister of Jessica Simpson, has ecstatically announced this evening that she and music icon Diana Ross' son Evan are engaged.

The tweet announcing the engagement came complete with arty romantic photo of the almost high-powered couple.

Simpson, 28, was previously married to rocker Pete Wentz, with whom she has a son, Bronx, 4. After her 2011 divorce, she began dating "Boardwalk Empire" actor Vincent Piazza, but they split last year.

The two were first spotted as a couple in July, but it already seemed serious, because they went out twice in 24 hours, including a late night at Teddy's, the club at Hollywood's Roosevelt Hotel.

Later that month they attended a party celebrating the Jessica Simpson Collection's fall line together; the singer is the face of the campaign. (Jessica Simpson, 33, who welcomed a son, Ace, last month, was the creative director.)

"Ashlee was there for work, so she was mingling with the guests," a fellow partygoer told ABC News at the time. But "Evan was supportive and stayed by her side. They're a very cute couple!"

Throughout the bash, they held hands and "were affectionate," but mostly stayed low-key with their PDA. "It was cute," the source added.