It was also an unexpected honour for Prashant's companions, finalists Ankita Mishra and Deepali Kishor, when all three were invited to the prime minister's official residence in Baluwatar Saturday morning.
"The prime minister asked me how I felt after winning the contest, " a beaming Prashant said after the meeting.
"Then he put the Nepali topi on my head and gave me his blessings. "
Koirala, who was wearing the black cap that is an integral part of his public persona, put a traditional Nepali cap on the head of the 24-year-old rising star, watched by smiling family members and Home Minister Krishna Prasad Sitaula.
Prashant, who had serenely faced a nearly three-month long nerve-racking contest by Sony Television channel to be selected winner from out of nearly 23, 000 aspirants, said he was nervous when he met the prime minister, since it was his first meeting with a leader about whom he had heard so much.
Music, he said with his trademark grin, had strengthened ties between India and Nepal. In response to coaxing by media persons, he sang a few lines of the Nepali song, "Gorkhali ko chhoro mo", that had captivated the hearts of the Nepali-speaking diaspora during the contest.
On his maiden trip to Kathmandu, Prashant said he was overwhelmed by the love and support shown to him from Nepal and the effort made by Nepalis who used to go to Darjeeling to send SMS votes for him.
Sidestepping political questions, Prashant said he had joined the contest urged by friends who used to tell him he should try his luck.
He had also filled up the form for the Zee Saregama contest, another popular talent hunt show, but could not go for it as the audition was postponed.
"I joined the 'Indian Idol' contest without thinking of winning, " he said frankly. "But after I reached the top three, I realised a lot of people wanted me to win. "
Regretting that he was not a trained singer, Prashant said he would like to have some training now. However, he was not sure immediately whether he would give up his job with Kolkata Police.
"I am grateful to my superiors who gave me permission to take part in the contest, " he said.
After a late night show at the Casino Royale following his arrival here Friday, Prashant -- along with Deepali, Ankita and Nepali pop star Nima Rumba -- was set to rock the capital at a mass concert Saturday afternoon.
Though it was raining heavily in the morning, diehard fans said they would certainly attend the concert being sponsored by ITC's joint venture in Nepal, Surya Nepal, to promote its newly launched brand of men's wear Springwood.
On Sunday, Prashant is scheduled to sing in Pokhara town before returning to Mumbai Monday.