According to Oregon State Police, the 52-year-old was "stopped for speeding and officers noticed that he was visibly intoxicated."
Per authorities, Thomas had a blood alcohol content of .11% and was issued a citation for a DUI. He was arrested and taken to the Grants Pass Sobering Center. Thomas' green Chevy Silverado was also towed.
Following the news, Thomas' father Thomas Sr., told TMZ that his "son has a serious problem and he needs help, and I hope he gets it." Thomas Jr.'s sister Samantha added that her brother's "drinking is not related to Meghan. He always drank."
Earlier this week, Thomas Jr. made headlines when he told The Daily Mail that he proposed to girlfriend Darlene Blount — and he looks forward to (hopefully) seeing the Duke and Duchess of Sussex on their big day.
"Absolutely I think our wedding will bring the family closer together," he told the news outlet of Markle's wedding invite.
Fox News' Jessica Sager contributed to this report.