Rod, 74, has eight children with five different women, and had three unsuccessful marriages before finally settling down with Penny, 48, and marrying her in 2007. He and Penny share two sons together, 13-year-old Alastair and Aiden, eight.
But Rod remains on good terms with his exes Alana Stewart, who is Kimberly's mum, Kelly Emberg, and Rachel Hunter - and proved so by meeting up at Rod and Alana's daughter's party in Los Angeles.
Kelly, 60, who was never married to Rod but shares a daughter, Ruby, 31, with the "Sailing" hitmaker, shared an image of all four women on Instagram, which she captioned: "#happybirthday @thekimberlystewart ! Can't believe you are 40! You looked radiant last night! #birthdaybash. A mother's reunion!".
The photo is believed to be the first time that the mothers of seven of his eight children have been seen together.
Alana, 74, who was married to Rod from 1979 until 1984, and shares Kimberly and 39-year-old son Sean Stewart with the Maggie May musician, also shared some snaps of the celebration, including one of a smiling Rod with his daughter.
However, Rachel, 49, who shares Renee, 27, and Liam, 24, with the rocker, and was married to him from 1990 until 2006, has not posted any images of the bash on social media.
Kimberly, who turned 40 on Tuesday, August 20, capped off her week of birthday celebrations by attending The Rolling Stones' concert in Pasadena on Thursday.
The rock legend also fathered a daughter, Sarah, with art student Sue Boffey, in 1963, but she was raised by adoptive parents as the then teenage Rod could not afford to raise her. She reconciled with her father following the death of her adoptive mother in 2008.