Leicester Tigers have signed lock Sam Carter from Ulster and Tonga outside back Solomone Kata, following his release by Exeter.
Former Australia international Carter, 33, left the Super Rugby side for Ulster in 2019.
Kata, 28, scored four tries in 17 games in his solitary season with Exeter.
It was with the Brumbies, under McKellar in 2020, that Kata had returned to rugby union, having had a successful stint in rugby league which saw him go on to play for New Zealand.
"What you see is what you get with Solomone," McKellar told the Leicester website.
"He's a physical, tough player, who also possesses a good skillset and offers us a genuine point of difference, in attack and defence, in the midfield."
Kata says he "can't wait to be coached" by McKellar again, with Carter echoing the sentiment.
"I am excited to link back up with Dan after a few years together in the Brumbies and, after speaking with him, looking forward to being a part of what he is looking to build at the club," Carter said.
The duo join on the same day that outside back Harry Potter was released early from his Tigers contract to return to Australia.
Leicester finished third in the Premiership table and had their title defence ended at the semi-final stage by Sale Sharks.