Queen's Platinum Jubilee 'bittersweet' reminder for Cheryl, says source

The Platinum Jubilee is said to be a sad reminder for Cheryl about the state of

her career a decade ago, when she used to perform in front of large crowds including during Queen Elizabeth II's Diamond Jubilee.

The recent celebration of Her Majesty's 70th year on the throne has reportedly

left the former "Girls Aloud" singer teary-eyed and reassessing her career.

It reminded her of that time she sang with Gary Barlow at the palace in 2012.

"It seems like yesterday when Cheryl was performing with Gary Barlow at the palace

it really was one of the highlights of her career," a source told Heat magazine.

It is said that the "decade in-between has been tough, with highs and lows.

she feels like there have been some mistakes and missed opportunities."