Doncaster secured the services of Jack Roberts three months early as the centre has arrived on loan for the rest of the 2018/19 season, ahead of his permeant move in the summer to Castle Park.
The 27-year-old has Premiership experience with Leicester Tigers as he spent three seasons and made 36 appearances during his time at Welford Road.
The Welshman started his career at the Scarlets academy before moving to Llandovery and then to Championship side Rotherham Titans. Jack spent one season at the South Yorkshire side, making 29 appearances in all competitions and showed his talents and attributes that lead him to the Premiership with a move to Leicester Tigers in 2014.
Jack started four matches towards the end of the campaign, scoring on his debut in the 28-21 win over London Scottish.