The former dual-code England international left Wigan in controversial circumstances last June but, strangely, the two sides have not met since his switch.
Rovers, with new coach Tony Smith taking charge for the first time, host the defending champions on Sunday.
Second-row Tomkins, 32, had spent all his rugby league career at Wigan, playing more than 200 games for the Cherry and Whites over two spells either side of a stint in rugby union with Saracens.
Aside from an eight-game loan spell at Widnes Vikings in 2007, it was all he had ever known.
“It will be strange, no doubt about it,” he said, having won Super League, Challenge Cup and World Club Challenge titles with Wigan.
“I’ve got some really good friends in that team.
“Some people say once you cross the white line it’s just a shirt, but it’s not for me.
“I’ve experienced playing against my brothers but it will be different playing against friends.”
Tomkins concedes Wigan are playing a different style of football - more free-flowing - since Adrian Lam took over from his former boss Shaun Wane at the end of last season.
But with Rovers sat in 11th place just two points above the relegation spot following Tim Sheens’ sacking on Wednesday, he knows they have to concentrate on themselves.
Wigan have had their own struggles and are struggling in ninth just two points above KR.
“It will be a sweet one if we do get a victory,” said Tomkins, who returns from suspension to take his place in Smith’s first line-up.
“But genuinely for me it is just about getting the two points for Hull KR.
“It’s not really about Wigan, especially with the week we’ve had.
“It’s more about us sticking together as a team and getting a result.”
Rovers host Warrington Wolves next and then face a massive fixture at London.
“We are just concreting on this game,” insisted Tomkins.
“But to get a win this week and then go down to London and get a result then that really changes our position in the table.
“Moving forward, with 13 games left there’s a lot of games there that are wins for us if we improve as a team.”
Tomkins maintains Rovers - who have challenged in so many games - can swiftly turn things around.
“Catalans are third in the table - we’re second bottom - and they’ve been up and down with their form,” he said.
“So it’s not as though we’re so far behind teams that are above us.
“The table doesn’t lie in that it’s wins and losses, but if you look at the results we’ve been in a lot of close losses or games where we’ve been in front and ended up losing the game.
“If we were getting beaten by 50 points every week and second bottom then we’d be a bit more worried.”