The ex partners engaged in the 'emotional' conversation to acknowledge that the Duke of Sussex was officially moving on, Vanity Fair reported.
"It was their final call, a parting call in which they both acknowledged Harry was moving on," a "family friend" told the magazine.
"Chelsy was quite emotional about it all, she was in tears and almost didn't go to the wedding. In the end, she went and promised Harry she wouldn't try and gatecrash the party."
Chelsy, 32, did attend the church service at St. Georges Chapel in Windsor Castle, and the lunchtime reception hosted by Queen Elizabeth where all 600 guests were invited.
However, she was not invited to the evening party hosted by Prince Charles, where just 200 guests were invited.
Harry, 33, and Chelsy dated on-and-off for six years after meeting through mutual friends in 2004.