Researchers claim husbands and wives who bounce out of bed every morning are more prone to be love rats after work.
Psychologists claim people who wake up early are more likely to CHEAT on their partners.
The Morality of Larks and Owls study examined the relationship between ethical decision making and people's "chronotype" - which is when individuals are most likely to want to be asleep.
Psychologists say early-rising 'larks' and late-night 'owls' have different levels of honesty depending on the time of day.
Experts say people are at their most honest when they have the most energy – with night owls more likely to be faithful at night.
The findings suggest that a human's body clock could be linked to two timing and give hope to people who have been branded as having fewer moral constraints for getting up at midday.
The study concludes: "In the morning, evening people are more unethical than morning people.
"They cast doubt on the stereotype that evening people are somehow dissolute."