The former Dawson's Creek actress - who has filed for divorce from the 'Rock of Ages' star after five years of marriage - felt like she had changed 'so much' in her time with Tom.
Sources close to the 33-year-old, who played innocent Joey in the popular teen drama, told friends she had found her relationship with the megastar, 49, had become 'too much' for her.
A source said: 'After five years of this Katie really felt like she was going crazy and that she was actually turning into the robot that the press had always made her out to be.
'Katie has actually got a great personality and she used to be spunky and feisty. She changed so much when she was with Tom, she became downtrodden and insipid.
'In the end it just got too much, she was sick of it and decided she had to do something. Basically, she grew up and lost the starstruck goggles she had been wearing.'
Katie is reportedly seeking full custody of their six-year-old daughter Suri after beginning to question her life with Tom and his control of their decision making.
The source added to RadarOnline.com: 'Katie did not want Tom making all the decisions in Suri's life, and that's what was going on. She decided it was high time she started deciding on what was best for her daughter, or at least having an equal say, and she knew that would be impossible if she remained Mrs. Tom Cruise.'
Holmes's lawyer Jonathan Wolfe made it clear what his client's priority is in a statement to People magazine: 'Katie's primary concern remains, as it always has been, her daughter's best interest.'
© SMGSplit: Katie Holmes felt like 'a robot' because of Tom's controlling ways
A source told RadarOnline.com: 'It's been tough for them over the past five years to watch Katie be controlled by Tom and they really felt that they had lost their daughter to some extent.'
'So, that's the one bright side to the divorce - they feel like they're getting the old Katie back again.'
But it does appear that Tom really was blindsided by his wife of five years, as he gushed about her at a ceremony to accept his Friars Club Foundation Award just two weeks ago.
Tom who took his children Suri, 6, and Connor, 17, as dates to the event, said after he picked up his award: 'My wife who couldn't be here tonight, I have to thank, she made this suit for me. She's amazing. I'm very lucky to be married to her.
He then added, according to Usmagazine: 'She's in China working.'
'And my oldest daughter, Bella, couldn't be here. She's also working. The women are all working!'
The actress filed documents in New York this week citing 'irreconcilable differences'.
She has asked for legal custody, primary residential custody and a 'suitable amount' of child support from her husband, TMZ reports.
Miss Holmes is also asking for a division of property in the divorce documents, although there is a significant pre-nuptial agreement that is based on California law.
The couple are worth around $275 million - much of that owing to Tom's box office success.
The terms of the pre-nup are understood to be clear - for each year the couple stay married, the Dawson's Creek actress collects $3million - to a maximum of $33 million after 11 years - as well as their palatial home in California.
If their marriage had lasted more than 11 years, Holmes would have received half of Cruises's reportedly $250 million fortune.
After filing for divorce less than six years later, according to the agreement, Katie should only be entitled to $15 million as well as the couple's $35 million Beverly Hills Mansion
Their daughter Suri
Cruise is believed to have 'not seen' the divorce coming.
But sources insist that she did tell her husband of five-and-a-half years that she was filing for divorce - but she didn't give him a chance to control the spread of the news, as he did with Nicole Kidman.
The fact that she issued a solo statement speaks of some heat around the final extinguishing of the marriage.
However, Mr Cruise's shock is to be believed considering the fact that the pair were spotted together in Iceland around two weeks ago, holding hands.
Nevertheless, Miss Holmes failed to turn up to at any of the worldwide premieres of her husband's latest film Rock of Ages, despite Cruise's constant protestations of love for his wife.
The final arguments seem to have been over where Cruise was going to spend his 50th birthday on Tuesday. He told her that he was planning to be on the set of his latest film Oblivion, in Iceland, and that seems to have been the last straw.
The statuesque brunette had frequently been pictured looking drawn and exhausted during her marriage. One Hollywood source said she had been 'utterly miserable with Tom for months, if not years'.
Indeed, the row over his birthday followed another bust-up over what Miss Holmes felt were embarrassingly bad taste pictures of him on the cover of W magazine last month.
© WCover boy: Tom's pose on W magazine is said to have infuriated Katie
Miss Holmes, a nice girl from Ohio who is nevertheless very aware of why Cruise feels the need to play the macho card in public, was apparently 'speechless' with disgust and felt the pictures laid both of them open to ridicule.
The marriage has been in such poor shape that for the past year they have led almost entirely separate lives.
Miss Holmes has chosen to stay with Suri in Cruise's New York apartment while he has travelled the world working.
The little girl has been her constant and only companion. They are often out together until late, and Miss Holmes - who gave up all the threads of her old life to become Mrs Tom Cruise - seems to have no other friends at all.
A shopping and sundries budget reputed to run at $125,000-a- month (£80,000) could only keep her amused for so long.
© Hennessy/lawrence/SplashFocused on work: Tom was pictured on filming his new movie Oblivion in Iceland on Wednesday
Another source added: 'Katie spent her time avoiding him, and they rowed terribly.' When Cruise was filming Rock of Ages in Miami, Miss Holmes came along with Suri and they made a family holiday of it. But since then they have spent no more than a handful of nights under the same roof.
Miss Holmes, who used to have a poster of Cruise on her bedroom wall, found that being married to an intense, workaholic, and deeply religious megastar was no picnic.
In pictures of her going about her daily business she looked completely worn out. Her brown hair was prematurely grey, she never wore make up. One shapeless cardigan was succeeded by another baggy jumper.
© SplashKatie, seen here with Suri on June 26
Her once promising film career - she had been the love interest in Batman Begins - had been stifled. Roles evaporated. She ended up trying to find work as a fashion designer, endorsing the line Holmes and Yang.
The bigger picture is that this is the end of the third of Cruise's marriages and a spectacular failure of his strategy to relaunch himself as a 'regular guy'.
And if the union was supposed to cease gossip about Cruise and his personal life, in particular rumours of his homosexuality - always denied - it failed utterly.
The couple's 2006 Italian wedding was choreographed like a massive movie premiere, with more bodyguards than guests and the ultimate goal seemingly the fantastically romantic images which were released to the media of the A list star and his pretty bride.
© Getty'Dream wedding': The pair married in an Italian castle in 2006
When the romance began - Katie had met Tom to discuss the possibility of appearing in Mission Impossible III - she was immediately sent on an intensive and lengthy study course about Scientology, the religion founded by sci-fi author L Ron Hubbard in 1954, which holds that humans are descended from an exiled race of aliens called Thetans.
She was 'audited' by Scientology counsellors, and unlike Penelope Cruz and Nicole Kidman before her, has totally embraced the movement.
Cruise proposed on June 17, 2005 on the top of the Eiffel Tower following a famously embarrassing declaration of his love on Oprah Winfrey's show, where he jumped up on the couch yelling 'I'm in love, I'm in love, I can't be cool, I can't be laid back.'
Despite earlier reports that there would be a Roman Catholic ceremony of some sort - Katie was born a Catholic - it was a Scientology wedding. What's more it was conducted by David Miscavige, Tom Cruise's best friend who is the head of the movement.
From the outset Miss Holmes struggled to ever settle in their Los Angeles mansion. Cass Mapother is a key figure here, Tom's sister - and she and her three sons share the house with Tom and his two adopted children Conor, 17, and Isabella, 19. But Miss Holmes never felt that the massive mansion, stuffed with bodyguards, was her home. Everyone who came through the doors was a Scientologist.
© WENNCrazy in love: Tom, giddy over his budding relationship with Katie, famously jumped on Oprah Winfrey's couch in 2005
You wonder, though, if he will be all the more damaged still by what has happened to Katie Holmes.
Before they met she was a natural beauty, and her physical decline in the five and a half years that followed is almost shockingly obvious.
How will Tom - the sofa jumper who wants so desperately to be loved - ever get over this?
© Vanity FairProtesteth too much? The couple presented their daughter to the world on the cover of Vanity Fair in 2006, five months after her birth
Who actually gives a toss.
These trials affect millions everyday,it matters little that they are celebrities,I'm sure they'll be re-hitched with latest manufactured heartthrobs within 3 months with all the glam magazines in hot pursuit.
Once upon a time it would have been considered shameful to waste everyone's time with empty promises on wedding day (for as long as we both shall live etc etc).