The brief and brutal primary battle between Newt Gingrich and Mitt Romney wasn't exactly remembered for its kumbaya moments. 

Accordingly, Gingrich said Sunday he really doubts he'll end up as his ex-rival's running mate. 

"I think that's highly implausible," Gingrich said on NBC's "Meet the Press." 

The former House speaker said he's learned to never say never, but told the interviewer, "I find that as implausible as you find it." 

Still, Gingrich, who initially seemed to equivocate on his support for Romney after bowing out of the race in April, made clear Sunday that he's "totally committed" to Romney's candidacy -- even if he doesn't foresee joining the ticket. 

"He's tough. He's much tougher than I thought. He's prepared to do what it takes to win," Gingrich said. 

As for his own campaign, which ended millions of dollars in debt, Gingrich said he has "no regrets." 

"It was a wonderful, amazing experience," he said, adding that his wife "says she learned two big things -- people are overwhelmingly nice, even if they don't agree with you, and money matters."