TMZ reports that Kevin's wife, Christine Baumgartner, has filed for divorce after 18 years of marriage.
The 68-year-old actor married the 49-year-old model and fashion designer in 2004. The couple, who began dating in 2000, tied the knot at Kevin's Aspen, Colorado ranch. Citing 'irreconcilable differences,'
Christine is seeking joint custody of their three children, Cayden, 15, Hayes, 14, and Grace, 12.
Kevin filed his response to the divorce on Tuesday, also requesting joint custody. A statement from Costner's rep read: "It is with great sadness that circumstances beyond his control have transpired which have resulted in Mr. Costner having to participate in a dissolution of marriage action."
The statement concluded by asking for privacy for the couple, and their children during this challenging time.
Christine is reportedly not seeking spousal support, with Kevin's response filed by Laura Wasser.
Laura indicated that a prenuptial agreement exists between the two, stating, "Spousal support to be payable to petitioner pursuant to the terms of the parties' Premarital Agreement."
Kevin was previously married to Cindy Silva from 1978 to 1994, with whom he shares three children - Annie, 39, Lily, 36, and Joe, 35. He also has a son, Liam, with Bridget Rooney, whom he dated after his split from Cindy.
This news comes after new details about Kevin's rift with Yellowstone creator Taylor Sheridan.
Sources claimed that Sheridan's alleged "God complex" has left Costner frustrated with the development of the hit Paramount Network series. There are also reports that Costner's character, John Dutton, may be killed off in the second half of Yellowstone's current fifth season.
The first half of the season ended on New Year's Day, with the second half initially scheduled to premiere this summer, though that timeline now seems uncertain.
Kevin, who is directing his Western saga Horizon, reportedly wanted to film the second half of the season for only one week.
It remains unclear when production on the new episodes of Yellowstone Season 5 will begin, or if they will indeed feature the death of John Dutton.
Read more HELLO! US stories here
Keep up with the latest celebrity stories Sign up to our HELLO! Mail newsletter to receive the latest news straight to your inbox.