19-Year-Old 'Duck Dynasty' Star John Luke Robertson Is Engaged

— -- When you know, you know.

Nineteen-year-old "Duck Dynasty" star John Luke Robertson popped the question to his girlfriend Mary Kate McEacharn over the weekend and -- of course -- she said, "Yes!"

He did it on his 19th birthday. Talk about the best present ever.

"Happy Birthday to the boy I'm going to marry," McEacharn wrote on Instagram.

The couple also posted a cute picture of Robertson holding up a sign that read "Future Mrs. Robertson," with an arrow pointing to McEacharn, while she shows off her engagement ring.

Luke is the grandson of Phil Robertson, the patriarch of the family. John Luke and Mary Kate started dating earlier this year.

He posted the same picture with the caption, "She. Said. Yes."

"I am so excited to marry my best friend," John Luke tells US Weekly via a statement. "I know my parents married young as well, and they have always been examples of what 'could be' to me. Fast-forward 22 years and they are more in love than ever, and I hope Mary Kate and I are the same way in the years to come. God has truly blessed us."