The source added: "She has been a private friend not many people know about."
The couple - who have six-year-old daughter Suri - reached a private divorce settlement on Monday less than two weeks after they split.
It is believed Holmes will get primary custody of Suri and continue to live with her in New York City, with Cruise allowed generous visitation rights, although representatives of the pair are yet to confirm any details of their settlement.
But the couple did release a joint statement earlier this week insisting they are "committed" to working on their daughter's "best interests".
They said: "We are committed to working together as parents to accomplish what is in our daughter Suri's best interests. We want to keep matters affecting our family private and express our respect for each other's commitment to each of our respective beliefs and support each other's roles as parents."
HOLMES REGISTERS WITH CATHOLIC CHURCH
Katie Holmes has registered with a Catholic church in New York.
The actress appears to have formally confirmed her return to Catholicism by signing up as a member of the congregation of the Church of St Francis Xavier, which is located on 16th Street between Fifth and Sixth Avenues.
One member of the church choir told the Huffington Post: "Everyone is thrilled to have Katie join us. She has not yet attended a service, but when she does she will be welcomed with open arms."
It has been widely speculated that Holmes wanted to protect the couple's six-year-old daughter Suri from being exposed to Scientology, but Cruise's lawyer Bert Fields is adamant religion played no part in the 33-year-old actress' decision to file for divorce from her husband.
He told RadarOnline: "Let me be very clear about this. The Church of Scientology played absolutely no role in the divorce settlement talks at all. Period.
"The mere suggestion that the Church was involved in any element of the talks and ultimate settlement is categorically false. Anyone suggesting otherwise is just wrong (sic)."
HOLMES USED DISPOSABLE PHONE - REPORT
Katie Holmes used a disposable mobile phone to initially arrange her divorce from Tom Cruise.
Holmes reportedly used the throwaway gadget, provided by a friend, to start negotiations with her lawyers without him knowing.
A source told the Los Angeles Times that the brunette star took the course of action to prevent Cruise or his staff finding out about her intentions, which meant she was able to hire three law companies in three different states by the time a deal was agreed to end their marriage.
- Bang! Showbiz
