The legendary comedian was also joined by Robert Downey Jr., who stars in the Iron Man films alongside Paltrow and was seen driving up to the private location.
“Nothing beats a great night with an old friend,” Lowe, 54, wrote alongside the image. “RDJ, I luv ya!”
In a sweet gesture of friendship, Diaz, who tied the knot in 2015, supported her pal by giving Paltrow helpful advice leading up to the ceremony, a source told PEOPLE.
“Cameron was very excited about Gwyneth’s wedding,” said an insider. “Gwyneth has been giving her updates and asking for advice during the planning.”
The source added, “Cameron pulled off a private wedding even though the media found out about it before. Gwyneth wanted the same privacy.”
Of course, Paltrow’s mother Blythe Danner was also on hand as she watched her daughter walk down the aisle.
“It was gorgeous — the most beautiful wedding I’ve ever seen,” Danner, 75, told photographers during a casual stroll on Sunday.
Director Steven Spielberg and his wife Kate Capshaw also attended the private ceremony.
Paltrow and Martin share 14-year-old daughter Apple and 12-year-old son Moses. Falchuck also has two children from a previous marriage, son Brody and daughter Isabella.
The couple announced the exciting news on the cover of Paltrow’s Goop Magazine‘s Sex & Love issue after dating for over three years.
Paltrow opened up about planning her wedding in January, admitting to PeopleStyle she was giddy thinking about what her nuptials would look like.
“I’m excited about everything! I’ve never had a wedding before. So even though I’m 45, I sort of feel like a 21 year old,” she said. (Paltrow previously eloped with ex-husband Chris Martin in 2003.)
The actress revealed she had fun brainstorming with her best friends about planning her wedding.
“It’s kind of fun to talk about with my girlfriends,” she said. “They send me pictures of dresses — they’re as excited about it as I am. It’s pretty cute.”