After four years of marriage Country couple Miranda Lambert and Blake Shelton announced on Monday that they were calling it quits on their marriage.

Although they did not reveal the reason for their split, a source explained to E!Online that the couple's busy schedules was a factor. They spent a lot of time away from each other, which reportedly gave rise to trust issues as well.

"Their busy schedules were a big issue for them. They both worked a lot and had to spend a lot of time apart. The less time they spent together, the more they grew apart," the source shared.

"Trust was an issue for both of them. It went along with having to spend a lot of time apart. Rumors of infidelity put stress on them. Despite denials, even just rumors of cheating are still hard to hear," the source added.

News of their split came as a shock to many, as in recent months both Shelton and Lambert had tried hard to prove there was nothing wrong in their marriage. However, their four years of marriage has constantly been plagued with infidelity rumours.

For instance, in 2013 "The Voice" judge was accused of flirting with singer Cady Groves on Twitter. However, he insisted there was nothing inappropriate in their relationship.

And earlier this year, Lambert raised eyebrows when she was allegedly spotted flirting with country crooner Chris Young.

Lambert and Shelton announced the split through a joint statement saying this wasn't the way they wanted their future together to end.

"This is not the future we envisioned," read a statement to the Associated Press. "And it is with heavy hearts that we move forward separately. We are real people, with real lives, with real families, friends and colleagues. Therefore, we kindly ask for privacy and compassion concerning this very personal matter."