Jennifer Aniston and Brad Pitt
Brad Pitt says he was "wasting opportunity" while being married to Jennifer Aniston Reuters

While Jennifer Aniston and Justin Theroux's split came as a shock to many, speculations have been rife over what caused the couple to call it quits after less than three years of being married.

And, if a new report is to be believed, it boils down to tensions between the couple and some old post-it notes from Brad Pitt.

According to Us Weekly, The Leftovers actor had moments of insecurity during his marriage over what the website refers to as "sweet little Post-its".

"He stumbled upon old Post-it notes Brad had written," an alleged source dished adding, "Sweet little Post-its like, 'You looked nice tonight' or 'Miss you already.'"

Explaining the aftermath of this discovery, the magazine source further added, "Jen assured him they weren't a big deal, but Justin wasn't thrilled ... Justin had moments of insecurity like that."

However, now that both Anniston and Pitt and single, fans shouldn't be too optimistic about a possible reconciliation either. "She never talks about him. That chapter is sealed and in the past," another source was quoted as saying by E! Online.

This comes after the Friends alum announced that she and Theroux will be going their separate ways to continue with their "cherished friendship".

"In an effort to reduce any further speculation, we have decided to announce our separation," the couple announced via a joint statement on 15 February. "This decision was mutual and lovingly made at the end of last year. We are two best friends who have decided to part ways as a couple, but look forward to continuing our cherished friendship."

While this was the first marriage for Theroux, his soon-to-be ex Anniston was previously married to the Fight Club actor until their infamous split in 2005.

Following that divorce, Pitt was in a long-term relationship with actress Angeline Jolie. The couple, who share six children - Maddox, 16, Pax, 14, Zahara, 12, Shiloh, 11 and 9-year-old twins Knox and Vivienne – however, called it quits in September 2016.

Jennifer Aniston and Justin Theroux
Jennifer Aniston and Justin Theroux celebrated their second wedding anniversary on 5 August REUTERS/Danny Moloshok