Alpha Centauri ( The Curse of Peladon ) Alpha Centauri was the Alpha Centauran delegate to the planet Peladon . Biography . In 1881 , Alpha Centauri , answering to a distress call which the Twelfth Doctor had sent , was willing to help Empress Iraxxa off her desolated home planet Mars , and welcomed both her and her Ice Warrior s to the universe . ( TV : " Empress of Mars " ) Alpha Centauri attended Bernice Summerfield and Jason Kane ' s wedding in Cheldon Bonniface on 24 April 2010 . ( PROSE : " Happy Endings " ) Alpha Centauri first came to Peladon on the Committee of Assessment to review their petition to enter the Galactic Federation . They aided the Third Doctor in defeating Hepesh and Arcturus . ( TV : " The Curse of Peladon " ) Five years after Peladon joined the Federation , when Princess Lixgaar of New Mars was taken to Peladon for safety , Centauri locked the Princess away in the tower containing the chamber of the Prisoner of Peladon . They didn ' t wish to keep this a secret from King Peladon , but was insisted upon by the Federation council to " conceal the truth " . While hiding in the chamber with the Princess , the Third Doctor , who was with King Peladon , Lord Axlaar and Axlaar ' s accomplice , Sslurn , knocked at the double doors . Centauri opened the doors . The Doctor called for Princess Lixgaar within the chamber , whom Axlaar threatened with his sonic disruptor . The Doctor attacked Axlaar in the chest ; the blast of the disruptor hitting Sslurn . Axlaar took aim again at the princess , swatting the Doctor aside , and King Peladon threw himself at him in a blind rage . After this , Axlaar fell from the window . The next day , Centauri contacted Io . Izlyr arranged a Federation peacekeeping force to take the princess to safety . Centauri apologised for their betrayal to Peladon and announced their immediate resignation . Peladon suggested to Centauri that the refugees would need someone to grant them safe passage home and should relations between Peladon and the Federation continue , " we will need a full ambassador " . Meanwhile , the Doctor quietly left in the TARDIS . ( AUDIO : " The Prisoner of Peladon " ) When they became ambassador , Centauri again helped the Third Doctor , this time to defeat the plans of Eckersley and a group of renegade Ice Warrior s led by the Ice Lord Azaxyr . ( TV : " The Monster of Peladon " ) Centauri was also present during the Seventh Doctor ' s efforts to recover the Diadem from Nic Reece on Peladon in 3984 . They attempted to repeal the Doctor ' s execution alongside his companion , Bernice , with little success . ( PROSE : " Legacy " ) They were still serving as the Federation ambassador to Peladon into the 41st century , when they were nearing retirement age . At this time , they escorted Princess Pandora of Earth to be wed to King Pelleas , unaware that she was being led to her death at the hands of Sekhmet . They non - violently stopped Arktos from taking trisilicate from a sabotaged mining operation and helped the Fifth Doctor and Peri return to the TARDIS in orbit around Peladon as a small detour . Following the death of Pandora , as well as the Martian royalty , Prince Zixlyr and Princess Alixlyr , Alpha Centauri knew they had months of negotiation with the Earth and Martian governments to consider before retiring . ( AUDIO : " The Bride of Peladon " ) Characteristics . Alpha Centauri had a squeaky falsetto voice , and was a genderless hermaphrodite hexapod according to the Doctor . ( TV : " The Curse of Peladon " ) Nevertheless , the Doctor sometimes referred to them with masculine pronouns , and had a penchant for addressing them as " my dear fellow " . ( TV : " The Monster of Peladon " ) Like most of their race , Alpha Centauri was a natural pacifist and a hypochondria c . Despite this , they demonstrated and developed a degree of courage during their time on Peladon , including their success in capturing the known criminal Arktos when he tried to steal Peladon ' s mineral wealth during Sekhmet ' s escape . ( TV : " The Curse of Peladon " , " The Monster of Peladon " ) Behind the scenes . Due to their appearance in " Empress of Mars " , Alpha Centauri holds the title of the second longest interval between on - screen appearances , at 43 years . The number one spot is held by the Great Intelligence with 44 years and the Macra come in at third with 40 years . Axos had the longest wait to return in all media , with a thirty - nine year gap .