However, there were at least two people who saw it coming.
Threapleton's grandparents, Norman and Jean Threapleton, told the British tabloids that Winslet's huge success had placed enormous pressures on the young couple and that they believe the marriage fell apart due to diverging careers.
"She's a star while Jim is trying to make his way in his own field. Jim is a bit of a quiet type and I don't know whether all this theatrical and film life has gone down well with him. It's not really his thing," Norman Threapleton told the British Mirror.
"He wants to be recognized in his own right--write his scripts and get away from things--and not just be Kate's husband," he added.
Jean Threapleton also told the British Daily Express, "We have known for a little while that things [were] not good between them. Her work and his work often kept them apart. They seem to be under so much pressure that they don't have time for each other--her with her film career and Jim writing."
"Jim and I have great respect for each other. There's no malice. It's extremely sad but we're all fine. Jim and I are both communicating constantly."
She added that the couple's 11-month old daughter Mia, "remains a happy child that she always has been. That is all, and we would be grateful now if you would respect our privacy."
Winslet and Threapleton met on set of the independent film Hideous Kinky in 1998 and were wed later that year. Winslet often publicly spoke about how happy she was with Threapleton. The couple even bought a $1.17 million rural home in southern England last August in which to raise Mia.
However, friends and neighbors have reportedly talked about arguments and tearful bouts within the last few months.
"Kate believes their relationship has suffered a seismic fault. There's a lot of hurt there," the Mirror quoted an unnamed friend as saying.
BBC News reports that the pair will now consult divorce lawyers.