Kate Winslet is one of the biggest movie stars on the planet, but RadarOnline.com has exclusively learned the actress isn’t very friendly off-screen and even brushed off two teenage fans.

While flying on a Virgin Atlantic flight on June 11 from London to Boston, fellow first-class cabin fliers Susan Roberts and her two daughters Katie, 17, and Jenny, 14, noticed the Titanic star sitting just ahead of them and were saddened when they were snubbed by Kate.

“My two daughters asked for an autograph about half an hour into the six and a half hour flight and she told them she would come back later and visit. Well, that never happened,” Susan exclusively told RadarOnline.com.

“It was very sad that she couldn’t be bothered.”

However, Susan said a flight attendant did come back to tell the girls Kate would autograph a book for them, but that she would have to make the exchange — which she did for them.

“I am sad that she told the girls she’d visit with them. She could have just said she didn’t give autographs and the girls would have understood,” Susan explained.

“They would have been disappointed but not disillusioned.”

The experience has changed Katie and Jenny’s affection for one of their favorite actresses, Susan said.

“My daughters have dumped their Titanic and The Holiday DVDs vowing never to watch her movies again,” Susan revealed.

Susan also told RadarOnline.com that she’s flown Virgin Atlantic in the past and usually has great service, but that with Kate on the flight the attendants were preoccupied in making sure her every need was met and other passengers were ignored.

“It was also sad that the usually excellent service through Virgin Atlantic was nonexistent as the flight attendants spent the majority of their time providing Ms. Winslet with food, tea and alcohol and the rest of the first class cabin was left to fend for itself,” Susan said.

“The flight attendants even blocked the aisle where Kate was sitting.”

As RadarOnline.com previously reported, fans in Massachusetts claim they were also snubbed by Kate, 36, as they eagerly awaited her arrival on the set of Labor Day.

“Kate was so rude, she never once acknowledged any of us, I was devastated,” hopeful fan Shanna Swan told Star magazine.  “She gave dirty looks to people in my town who waited hours to see her.”