The couple celebrated their upcoming nuptials with family and friends on Saturday night at a party hosted by Carole Bayer Sager and her husband, Bob Daly, at their Los Angeles home.
ET spoke exclusively with Sager, who first met Lopez through her manager five years ago, following the bash and she shared how both she and her husband wound up hosting the extravagant affair.
"J.Lo and Alex were here one night actually last November... for dinner and we had a great dinner and J.Lo and Alex wanted to see the house and look outside and see the land," Sager recalled. "Bob was showing them and as they walked outside I said, 'Hey if you guys ever get engaged we'll throw your engagement party.' So everybody laughed and I winked at J.Lo and that was the end of it."
"Then J.Lo... FaceTimed me the night she got engaged to show me her beautiful ring and I was thrilled," she continued. "About three weeks later J.Lo's manager, Benny Medina, called me and said, 'Hey did you mean that when you said you'd throw J.Lo and Alex an engagement party?' I said, 'Of course.'"
As for the guests at the event, which featured projected roses on the walls, as well as candles and flowers throughout the room, Sager told ET that "it was primarily J.Lo's family, Alex's family, and friends they've had forever."
"It was so nice because it wasn't about celebrities, it was about warmth and love and connection. I think they know that everybody had a fantastic time.... It was just a great night," she said. "There was lots of love in the room and their children -- Alex's children, J.Lo's children -- both of their mothers, J.Lo's father, were all here. I think it was just a special way to celebrate two very special people."
During the event, Sager told ET, Lopez sang "a little bit" of Journey's 1983 track "Faithfully," her daughter, Emme, snuggled up to her, and Rodriguez "made a beautiful toast" that left Lopez "a little bit teary."
"... They provide the love, I supply the setting," Sager added of the party. "It was wonderful. It caught some magic."
Sager -- who said Lopez refers to her as "her fairy godmother" thanks to her advice about life and love -- was clearly happy to host the affair, as she truly believes in Lopez and Rodriguez as a couple.
"I think when you come to a relationship as equals it's a much easier way to maintain, because you're coming to a relationship where you are both whole people... as opposed to people with holes," Sager explained. "They’re not looking to each other to fill in what they don't have within themselves, they can bring their wholeness to each other and become more... I think they are very much in love."
To show their thanks for the shindig, Lopez and Rodriguez sent their hosts a bouquet of flowers unlike anything Sager "had ever seen."
"It was insane," she said of the thank you gift. "Three men came to put it together and [it's] still very much alive in our atrium. [It's] so beautiful, so over the top, but just really appreciate it."
On Sunday, Lopez took to Instagram to share a few dazzling photos from the soiree.
"Thank you Carol and Bob for the most beautifully elegant night...we love you 🌸 💗#engagementparty @carolebayersager @arod," she wrote alongside a lovey-dovey shot of her and Rodriguez sharing a romantic kiss during the evening, with her gigantic engagement ring in full view. Carole Bayer Sager helped throw the star-studded bash, which was attended by Leah Remini, Ryan Seacrest, Benny Medina, Angelo Pagan and more.
J.Lo next shared a precious family photo of her daughter, Emme, and A-Rod's daughter, Ella, hugging the couple, while the former baseball star shared a snap of himself and Lopez smiling ear-to-ear.
See more photos below:
Rodriguez and Lopez's engagement party comes six months after he proposed in March. And while it seems the Hustlers star's son, Max, wasn't photographed during the party, Lopez recently told ET that he'll have a large role in the wedding.
"Of course," the actress gushed when asked if Max will be walking her down the aisle.
As for when and where the superstar couple will tie the knot, Lopez admitted they're still not sure.
"We're talking about it, but we don't have any firm plans... and we're talking about a lot of places [to get married in], but I don't know yet," she expressed. "We can't narrow it down yet."
See more in the video below.