Sean Lowe, Catherine Giudici and Ali Fedotowsky
05/14/2013 at 09:25 AM EDT
It was a Bachelor
party at the Thompson Beverly Hills hotel rooftop on Saturday.
and fiancée Catherine Giudici
bonded with former Bachelorette
, Ali Fedotowsky
, when the trio attended the fifth annual On the Go Mother's Day event.
At the pool party, Fedotowsky – who showed up sans new beau
Kevin Manno – "grabbed Sean and Catherine and congratulated them on everything," an onlooker tells PEOPLE. "Sean spoke about his recent stint
on Dancing with the Stars
and he and Catherine joked about them having choreographed a wedding dance."
Adds the observer at the Joico and Olay-sponsored event: "The couple seemed happy and definitely in love. Catherine mentioned that she wants a very mellow and intimate bachelorette party."