The exes tied the knot in April.
"Chris and Lukas haven't been getting along recently and things haven't been great between them," a source tells ET in the wake of the split. "It got worse and they decided it was best to end their relationship."
In court documents obtained by ET, Appleton, 40, cited "irreconcilable differences" as the reason for his split from Gage, 28. Their separation is listed as Nov. 10.
A source previously told ET that Gage and Appleton, who were first linked earlier this year, "got engaged" around the time they were in Mexico together in February.
Prior to their split, both men publicly gushed about their romance.
"I'm very happy. Very much in love and I feel very grateful to be able to share my time with someone very special," Appleton said during a March appearance on The Drew Barrymore Show. "Love is a really special thing and I think meeting someone you connect with is really, really special."
"I feel very happy, very lucky and very much in love," Gage echoed on the Today show later that month. "... We have fun together. We go on adventures. It's the best."