The 66-year-old actress played the second version of Romana in the BBC series opposite Tom Baker’s seventh Doctor between 1979 and 1981.
Lalla took over the role of the Doctor’s assistant from Mary Tamm, who originally portrayed the steely Time Lady, after she departed the part.
She made her debut in the serial Destiny of the Daleks, however she had already starred in Doctor Who as Princesss Astra in the story Warriors’ Gate.
During her time on the show, Lalla’s version of Romana and the Doctor went on a number of adventures including the City of Death which featured an alien called Scaroth, played by Game of Thrones star Julian Glover.
While starring in Doctor Who, Lalla ended up in a relationship with her co-star Tom, 83, and the couple got married in 1980.
Sadly, the relationship did not last and the pair split up two years later, Lalla later went on to tie the knot with author Richard Dawkins.
After leaving Doctor Who, Lalla has a number of roles including TV movie Schoolgirl Chums and Riviera.
However, she had not completely left behind the TARDIS and reprised her role as Romana in a series of audio adventures for Big Finish.
She also made a cameo in the Doctor Who 50th anniversary parody The Five(ish) Doctors Reboot.
Lalla has now become a writer and penned two books about knitting and one about embroidery.