The couple were joined at the bash 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.
"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 others friends and family well.
The party was a fun celebration and a preview of what's to come with the wedding," a source said. Timberlake, who proposed to Biel five years after he first started dating her in January 2007 - wore a black suit, while his 30-year-old fiancee wore a leopard-print halter dress teamed with hot pink shoes and a belt.
"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 source added.
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