About 47 foreign delegations including 23 heads of State or their deputies joined thousands of Kenyans to witness the swearing-in of President Uhuru Kenyatta for his second term in office.
Tanzanian President John Pombe Magufuli, however, skipped the event, despite earlier confirmation that he would attend.
Instead, Tanzania sent vice president Samia Suluhu to represent President Magufuli at the ceremony.
Of the six-member East African Community (EAC), only three presidents were present to witness the swearing-in. They are presidents Yoweri Museveni of Uganda and Rwanda's Paul Kagame and South Sudan's Salva Kiir who was the first to arrive in Kenya on Sunday.
Other heads of state from Africa who attended the ceremony were Ethiopian Prime Minister Hailemariam Desalegn, Mohammed Abdullahi “Farmajo” Mohamed (Somalia). Ismail Omar Gulleh (Djibouti), Ian Khama (Botswana), Ali Bongo Ondimba (Gabon), Hage Geingob (Namibia) and Edgar Lungu (Zambia).
Nigeria sent its vice president Yemi Osinbajo while former South African President Thabo Mbeki and his Ghanaian counterpart John Dramani Mahama also attended the inauguration.
“Several countries from America, Europe, Middle East and the Far East have sent powerful delegations to represent them at the auspicious occasion,” State House said in a dispatch.
Burundi's Pierre Nkurunziza, a member of the EAC bloc, also failed to turn up.
But it was President Magufuli's absence that raised eyebrows.
Kenya and Tanzania have had frosty trade and diplomatic relations following the election of President Magufuli in October 2015, derailing business between the two neighbours to the detriment of entrepreneurs who depend on it.
"This is not the right thing for President Magufuli. His absence will even intensify rumours that he sided with Raila Odinga during the electioneering period in Kenya," Justin Ole Ngeresa, an Arusha-based NGO official, told Tanzanian newspaper The Citizen.
While President Magufuli's friendship with Kenyan opposition leader and Mr Kenyatta's arch-rival, Mr Odinga, is not a secret, the Tanzanian leader has not publicly endorsed the latter.
However, there has been speculation that their rapport was the reason for an incessant diplomatic war between Kenya and Tanzania that caused the breaking of ranks on regional projects like the pipeline, the standard gauge railway and the trade partnership with Europe.
For a long time, Tanzania has been Kenya’s second largest export market after Uganda, underlining its importance as a trading partner.
In the five months to August, Kenya’s exports to Tanzania fell by 34 per cent to stand at $79.3 million compared to a similar period last year.
For President Nkurunziza of Burundi, he has not be comfortable travelling outside his country since the 2015 failed coup following his decision to seek a controversial third term that has led to a long-drawn political crisis.
-Reported by Edwin Mutai, Fred Oluoch and Zephania Ubwani.