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Tyler Christopher -- best known for his appearances on "General Hospital" over the course of 20 years -- may have had too much fun celebrating turning 47 ... because he ended up in jail.

The soap star was arrested in Martinsville, Indiana Monday night -- on his 47th birthday -- and booked for public intoxication. According to Morgan County Jail records ... he's being held on $225 cash and $1,000 bond.

As far as we can tell ... Tyler hasn't been released yet.

Based on his mug shot, Christopher's changed his look quite a bit since he left his role on another popular soap opera, "Days of Our Lives," earlier this year ... and not for the better.

Tyler played Stefan DiMera on 'Days' from December 2017 until leaving the series this past March. Before that, he played Nikolas Cassadine on 'GH' off and on from 1996 to 2016.

All that pales in comparison to the best fun fact about Tyler though -- he was married to Eva Longoria from 2002 to 2004.

Happy birthday, bud?