The fourth series, which begins in November, will star Gillian Anderson as the former Tory prime minister, while Olivia Colman will reprise her role as the Queen.
According to The Telegraph, the writer said he was surprised by how much the two women had in common, despite their opposing views.
“When I found out that they were born only six months apart, that was a really big breakthrough for me.
The Crown season four is set during the end of the 1970s, as Thatcher leads the country into the Falklands War and the Queen looks to safeguard the line of succession by finding a bride for Prince Charles.