The couple were joined at the bash - which took place at the 'Social Network' actor's friend and HomeMint collaborator Estee Stanley's house in California - by 100 family members and friends, including Lance Bass, JC Chasez, Trace Ayala, Ellen DeGeneres and her wife Portia de Rossi and Amy Adams, for a "fun" celebration.

A source told UsMagazine.com: "Jessica and Justin were mingling both separately and together throughout the party. Jessica seems to be very close with Justin's friends and vice versa. You can see that they have been dating for a long time and really know each other's friends and family well. The party was a fun celebration and a preview of what's to come with the wedding."

Justin - who proposed to Jessica in December five years after he first started dating her in January 2007 - wore a black suit and fedora, while his 30-year-old fiancee wore a leopard-print halter dress teamed with hot pink shoes and a belt.

A source said: "Justin and Jessica arrived at the party looking very excited. Jessica was stunning in a long dress with her hair down.

"Estee created a very warm, welcoming and festive party for the couple."

The guests were served gourmet appetizers by Wolfgang Puck Catering along with wine and champagne and enjoyed live music before a DJ took over to play popular hits from the likes of Usher, Madonna and Michael Jackson.

The source added to People.com: "Justin and Jessica danced and looked very happy."

Speeches then followed, with 31-year-old Justin appearing particularly "touched" by Timbaland's words.

The source remarked: "You could tell that they have a very special friendship."

The couple left the party at around 12.30am. (c) BANG