EXCLUSIVE

Katie Holmes is the one who filed for divorce and Tom Cruise was "blindsided" by Katie's legal move ... TMZ has learned.

We know Katie filed the divorce docs in New York on June 28, citing "irreconcilable differences." She is asking for sole legal custody and "primary residential custody" of the couple's 6-year-old daughter, Suri.

We also know Katie is asking for a "suitable amount" of child support .. this according to the divorce docs.

Katie also asks for a division of property in her divorce docs, although we know there was a significant prenup that is based on California law. Katie makes no mention of the prenup in her filing.

We're told Tom is "very sad" and "did not see this coming." He was spotted wearing his wedding ring just this week while filming in Iceland. Interestingly, Katie also wore her ring this week.

We're also told there is some "nastiness" here, evidenced by Katie's move to get sole legal custody.

Tom's rep has released a statement saying, "Kate has filed for divorce and Tom is deeply saddened and is concentrating on his three children. Please allow them their privacy to work this out."