Antonio Banderas and Melanie Griffith knew for a while they were going to separate. Credit: Frazer Harrison/Getty Images

After 18 years of marriage, Melanie Griffith and Antonio Banderas announced on June 6 they're separating. The decision to part ways, however, wasn't a surprising one. Griffith filed for divorce from the 53-year-old and although amicable, the split was "a long time coming," a source close to the couple tells Us Weekly.

"There was no cheating on either side," the source adds. "They had fallen out of love awhile ago."

The pair's rep said in a joint statement to Us on Friday, June 6: "We have thoughtfully and consensually decided to finalize our almost 20-year marriage in a loving and friendly manner honoring and respecting each other, our family, and friends and the beautiful time we have spent together."

The Working Girl star and Mask of Zorro actor, who wed in 1996, carefully considered their children, for one. "Their daughter Stella is about to be 18 in September and they wanted to wait until [the] kids were grown and out of the house before they split up, but knew they would awhile ago," the insider tells Us, "They stayed together for the sake of the kids."

In documents obtained by TMZ, Griffith is seeking child support and sole physical and joint legal custody of their 17-year-old daughter. The actress is being represented by famed celebrity divorce attorney Laura Wasser.

"They are committed to making the divorce go through easily and swiftly for the sake of everyone," the source adds. 

In an interview in 2011, Banderas admitted: "We have had as many problems as anybody. We've never hidden it."

This will be the fourth divorce for Griffith. The 56-year-old was married twice before to Don Johnson, and also to Steve Bauer. Banderas was previously married once before to actress Ana Leza.