Czech twins Filip and Patrik Twardzik have both signed contract extensions with Celtic.
Filip, who has made five first-team appearances and can play left-back or midfield, has committed his future until 2015.
Midfielder Patrik, who was a regular goalscorer for the Celtic Under-19s in recent seasons, has signed a one-year extension, tying him to the club until the end of next season.
The 19-year-olds first arrived at Celtic Park in 2009.
Filip, who is awaiting the results of a scan on a groin injury, told the Celtic website: "We have learnt a lot since we have been here. The physical side changed a lot, but we are still the same players we have always been, our bodies have just progressed.
"I want to stay in the first-team and hopefully win some more medals this year."
Patrik has set his sights on following his brother into the first team.
"I have always dreamt about being the best player in every age group so I want to get there," he said. "Filip is closer to it than me but I will get there."