Step into the size 15 shoes of one Mr. Walter Ray Allen for a moment and try to imagine what it’s going to feel like at 7:30 p.m. Tuesday.

That’s when the Heat’s pregame banner-raising and ring ceremonies begin before the season opener against the Boston Celtics at AmericanAirlines Arena. That’s when Allen will watch, along with his former Celtics teammates, as 12 of the Heat’s players from last season are honored at midcourt for winning the 2012 NBA championship.

The Heat survived Allen’s Celtics in an epic seven-game series for the Eastern Conference championship before running through the Oklahoma City Thunder in The Finals.

For about half an hour before the start of the 2012-13 season, Allen will feel more like a member of his former team than he will one of the new additions of the Heat. Then, just like that, Allen will have to flip a switch in his head and go head-to-head against his former mates.

No, this is not just any old season opener – not for Allen, not for the Heat and certainly not for the Celtics.

“I’m happy for them that they won, but at the same time they beat me and put us out, so I understand the emotions that Boston will feel watching the whole ceremony,” Allen said. “But at the same time, I’m excited for these guys.

“Once it’s over with, it’s business as usual.”

Take note of Allen’s pronouns usage in that quote. When he said “them” and “they” he was talking about the Heat. When he was referring to the Celtics, he used the first person, “us” and “me.”

SPLIT NOT AMICABLE

His identity, at least for a few moments Tuesday, will be a confusing mix of past and present, and that’s understandable. Allen wore Celtics green for five great seasons and was a cornerstone – along with Paul Pierce, Kevin Garnett and Rajon Rondo – in the rebuilding of Boston’s proud basketball legacy. Now, Boston is his main rival.

If wounds were beginning to heal in Boston after Allen’s move to Miami this summer, then the Band-Aids get ripped off Tuesday. Allen’s final game with Boston was a loss to the Heat in Game 7 of the Eastern Conference finals. His first game with the Heat is against the Celtics on the same floor.

“I’m not happy with him because he left but I still think he’s a great guy,” Celtics coach Doc Rivers said Monday. “And, eventually, we’ll all get over it.”

Eventually, but not Tuesday. The Celtics practiced at AmericanAirlines Arena on Monday due to the weather conditions in New England from Hurricane Sandy. Boston arrived in Miami on Sunday to beat the storm and the Heat was a gracious host, allowing their main Eastern Conference rival to use the arena in preparation for the season opener.

The upshot of that scheduling change was a larger-than-normal media throng for the Celtics’ practice. Media availability was packed and most of the questions focused on Allen’s move. It made for some awkward exchanges, especially for Rondo, who has been at the center of the storyline. For various reasons, the relationship between Rondo and Allen soured in their final two seasons in Boston. Locker room chemistry was partly to blame for the reason Allen took less money to sign with the Heat.

“It’s just another basketball game,” Rondo said, trying unsuccessful to dodge a question about the contentious undercurrent of Tuesday’s game. “It’s already going to be a heated rivalry because it’s two team that have been battling for the last three or four years. So ... that’s what it is.”

Like Rondo, Allen felt uncomfortable addressing the topic of his departure from Boston.

“I’d rather not discuss it,” Allen said. “I don’t think there was a No. 1 factor. It think it was a bevy of things that I had to [weigh]. So, I don’t think right now, in this setting, I want to discuss it.”

‘IT’S NOTHING PERSONAL’

Kevin Garnett, one of Allen’s closest friends during their time together in Boston, avoided questions about Allen completely.

“I’m going to play the game and get the [heck] up out of there, period,” Garnett said. “Play.”

Since his move, Allen hasn’t spoken with Garnett. On Monday, he passed it off as normal behavior between two opponents playing on rival teams.

“It’s nothing personal,” Allen said. “You want to beat the other team. I think with anyone who’s not on the Celtics, it’s always frosty. You don’t like the other opponent.”

While vague answers ruled the day, there was, and never has been, any doubt where Allen’s allegiance rests. It’s in Miami, with new teammates who are determined to give their reserve shooting guard a victory.

“We want to do it for [Allen], in a sense,” Heat star Dwyane Wade said. “The only thing we can do as teammates is just show him how much we appreciate him being here and that he made the right decision and that he feels that comfort from us.”