The two leading ladies were reportedly speaking over the phone for weeks in the lead-up to TomKat's divorce, quashing rumours they've been enemies since Katie and Tom hooked up in 2006.
"Nicole has been supportive, saying she's been through it too and to hang in there," a source told Us Weekly.
"She has been a private friend not many people know about."
And in another blow to Tom, 33-year-old Katie has reportedly ditched the Church of Scientology by registering with a Catholic church.
A member of the choir at the Church of St. Francis Xavier in New York 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."
Tom's dedication to the controversial religion is believed to be a key reason behind Katie's decision to file for divorce from her husband.
According to reports, Katie has an "ironclad" clause in her divorce settlement that prevents the couple's daughter Suri from being exposed to anything Scientology-related.
But while Katie has been reaching out for support, it appears Tom was determined to hide growing cracks in the couple's relationship in the weeks leading up to their split.
While staying in Iceland in June, the 50-year-old actor reportedly ordered his team to put duct tape over security cameras in their hotel room in an attempt to cover up their separate sleeping arrangements.
"Neither Tom nor Katie let on that they were having problems. It would have been a red flag if Katie had requested her own room," a friend of the couple's told the National Inquirer.
"So no one knows for sure whether they spent their final night together as husband and wife sleeping in the same bed, or if Tom had to sleep in another part of the suite. But they certainly kept up appearances."
And speaking of appearances, while TomKat reached an out-of-court settlement just 11 days after Katie filed for divorce, it appears the stress of the split is taking it's toll on the actress' well-being.
According to In Touch magazine, Katie's weight has "plummeted", with a friend of the star's revealing she has a "bony back."
"Like many people, she doesn't eat when she's stressed," said the friend.